<PAGE>   1
                                                                   EXHIBIT 10.8


                 FOURTH AMENDMENT TO SECOND AMENDED AND RESTATED
                                CREDIT AGREEMENT

         This FOURTH AMENDMENT TO SECOND AMENDED AND RESTATED CREDIT AGREEMENT
(this "Amendment") is made and entered into effective as of July 31, 2000 by and
among DYNAMEX INC. (the "Borrower"), a Delaware corporation, DYNAMEX CANADA INC.
("Dynamex Canada"), a federal Canadian corporation, DYNAMEX OPERATIONS EAST,
INC. ("Dynamex East"), a Delaware corporation (successor in interest by merger
to U.S.C. Management Systems, Inc., and Cannonball, Inc.), DYNAMEX OPERATIONS
WEST, INC. ("Dynamex West"), a Delaware corporation, ROAD RUNNER TRANSPORTATION,
INC. ("Road Runner"), a Minnesota corporation, NEW YORK DOCUMENT EXCHANGE
CORPORATION ("NYDEX"), a New York corporation, DYNAMEX DEDICATED FLEET SERVICES,
INC. ("Fleet Services"), a Delaware corporation, BANK OF AMERICA, NATIONAL
ASSOCIATION (successor by merger to NationsBank, N.A., which entity was
successor by merger to NationsBank of Texas, N.A.) ("Bank of America"), a
national banking association, FLEET NATIONAL BANK (formerly BankBoston, N.A.)
("Fleet"), a national banking association, BANK AUSTRIA CREDITANSTALT CORPORATE
FINANCE, INC. (formerly Creditanstalt Corporate Finance, Inc.)
("Creditanstalt"), a Delaware corporation, THE BANK OF NOVA SCOTIA ("Scotia
Bank"), a Canadian banking association, BANK ONE, TEXAS, N.A. ("Bank One"), a
national banking association, BANK OF AMERICA, NATIONAL ASSOCIATION (successor
by merger to NationsBank, N.A., which entity was successor by merger to
NationsBank of Texas, N.A.), as agent for itself and the other Lenders (in such
capacity, together with its successors in such capacity, the "Agent") and FLEET
NATIONAL BANK (formerly BankBoston, N.A.) and BANK AUSTRIA CREDITANSTALT
CORPORATE FINANCE, INC. (formerly Creditanstalt Corporate Finance, Inc.), as
co-agents (the "Co-Agents").

                                    RECITALS:

         A. Pursuant to that certain Second Amended and Restated Credit
Agreement dated as of August 26, 1997, by and among the Borrower, Dynamex
Canada, Dynamex East, Dynamex West, Parcelway Courier Systems (B.C.) Ltd. (a
British Columbia corporation that has now been dissolved), Road Runner, Bank of
America, Fleet, Creditanstalt, Scotia Bank, the Agent and the Co-Agents (as the
same has been and may be amended, renewed, extended, restated or otherwise
modified from time to time, the "Credit Agreement"), the Lenders agreed to
provide to the Borrower a senior secured revolving credit and letter of credit
facility (the "Credit Facility") in the maximum aggregate principal amount of
$75,000,000.

         B. Pursuant to that certain First Amendment to Second Amended and
Restated Credit Agreement dated as of May 5, 1998, the parties to the Credit
Agreement


FOURTH AMENDMENT TO SECOND AMENDED AND RESTATED CREDIT
AGREEMENT - Page 1
<PAGE>   2

amended the Credit Agreement to increase the maximum aggregate principal amount
of the Credit Facility to $115,000,000 and in certain other respects.

         C. Pursuant to that certain Second Amendment to Second Amended and
Restated Credit Agreement dated as of January 31, 1999, the parties to the
Credit Agreement amended the Credit Agreement to decrease the maximum aggregate
principal amount of the Credit Facility to $65,000,000 and in certain other
respects.

         D. Pursuant to that certain Third Amendment to Second Amended and
Restated Credit Agreement dated as of June 28, 2000, the parties to the Credit
Agreement amended the Credit Agreement to decrease the maximum aggregate
principal amount of the Credit Facility to $51,734,000 and in certain other
respects.

         E. The Borrower and its Subsidiaries, the Agent, the Co-Agents and the
Lenders have agreed, subject to the terms and conditions of this Amendment, to
further amend the Credit Agreement in certain respects as provided in this
Amendment.

                                   AGREEMENTS:

         NOW, THEREFORE, in consideration of the premises and mutual covenants
and agreements contained herein and for other good and valuable consideration,
the receipt and sufficiency of which are hereby acknowledged, the parties hereto
hereby agree as follows; provided, however, that this Amendment shall be, ipso
facto, null and void and of no force or effect if any of the conditions
precedent set forth in Paragraph 3 hereof are not fully and timely satisfied on
or before October 30, 2000 or if the condition subsequent set forth in Paragraph
4 hereof is not fully and timely satisfied on or before November 10, 2000:

         1. Terms Defined. Unless otherwise defined or stated in this Amendment,
each capitalized term used in this Amendment has the meaning given to such term
in the Credit Agreement (as amended by this Amendment).

         2. Amendments to the Credit Agreement.

         (a) Amendments to Certain Definitions. The definition of 'Swingline
Advances' is hereby deleted from Section 1.1 of the Credit Agreement and the
following terms and definitions set forth in Section 1.1 of the Credit Agreement
are hereby amended and restated to read in their entirety as follows:

                  "'Applicable Margin' means, for the period commencing with the
         Closing Date, the rate per annum set forth in the table below that
         corresponds to the ratio of (i) Funded Debt as of the date of the
         relevant financial statements referred to below to (ii) EBITDA for the
         four fiscal quarters of the Borrower and its Subsidiaries then most
         recently ended as


FOURTH AMENDMENT TO SECOND AMENDED AND RESTATED CREDIT
AGREEMENT - Page 2
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         of the date of such financial statements, calculated in accordance with
         Section 1.4:

<TABLE>
<CAPTION>
                                                                   Applicable Margins for
                                                                   ----------------------
                               Ratio of
                         Funded Debt to EBITDA             ABR Loans          Eurodollar Loans
                         ---------------------             ---------          ----------------
<S>                                                        <C>                <C>
                 Less than 1.50 to 1.00                        0.00%                3.00%

                 Less  than  2.00 to 1.00 but  greater
                 than or equal to 1.50 to 1.00                 0.25%                3.25%

                 Less  than  2.50 to 1.00 but  greater
                 than or equal to 2.00 to 1.00                 0.50%                3.50%

                 Less  than  3.00 to 1.00 but  greater
                 than or equal to 2.50 to 1.00                 0.75%                3.75%

                 Greater than or equal to 3.00 to 1.00         1.00%                4.00%
</TABLE>

         For purposes hereof and notwithstanding the preceding sentence, the
         Applicable Margin for the period from the Fourth Amendment Effective
         Date to the first Calculation Date thereafter shall be deemed to be
         0.75% for ABR Loans and 3.75% for Eurodollar Loans and shall thereafter
         be calculated on each Calculation Date based upon the preceding table
         and the financial statements delivered by the Borrower pursuant to
         Section 8.1(b) and the certificate delivered by the Borrower pursuant
         to Section 8.1(d); provided that if the Borrower fails to deliver to
         the Agent such financial statements or certificate on or before the
         relevant Calculation Date, the Applicable Margin shall be deemed to be
         the percentage reflected in the preceding table as if the ratio of
         Funded Debt to EBITDA were greater than 3.00 to 1.00 until the date
         such statements and certificate are received by the Agent, after which
         the Applicable Margin shall be determined as otherwise provided
         herein."

                  "'Commitment' means, as to any Lender, the obligation of such
         Lender to make Loans under the Revolving Loan Portion of the Loans and
         incur or participate in Letter of Credit Liabilities hereunder in an
         aggregate principal amount at any one time outstanding up to but not
         exceeding the amount set forth opposite the name of such Lender on the
         signature pages hereto (or any amendment hereto) under the heading
         'Commitment' or, if such Lender is a party to an Assignment and
         Acceptance, the amount of the 'Commitment set forth in the most recent
         Assignment and


FOURTH AMENDMENT TO SECOND AMENDED AND RESTATED CREDIT
AGREEMENT - Page 3
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         Acceptance of such Lender, as the same may be reduced or terminated
         pursuant to Section 2.12 or 11.2, and 'Commitments' means such
         obligations of all Lenders. As of the Fourth Amendment Effective Date,
         the aggregate principal amount of the Commitments is $19,500,000."

                  "'EBITDA' means, for any period, without duplication, the sum
         of the following for the Borrower and its Subsidiaries (or other
         applicable Person) for such period determined on a consolidated basis
         in accordance with GAAP: (a) Net Income, plus (b) Interest Expense,
         plus (c) income and franchise taxes to the extent deducted in
         determining Net Income, plus (d) depreciation and amortization expense,
         plus (e)other non-cash items to the extent deducted in determining Net
         Income, minus (f) non-cash income to the extent included in determining
         Net Income, plus (g) for any calculations that include the fiscal
         quarter ended (i) October 31, 1999, $241,900, (ii) January 31, 2000,
         $199,000, (iii) April 30, 2000, $259,200, or (iv) July 31, 2000,
         $290,700 (which amounts referred to in this clause (g) relate to
         extraordinary legal and accounting fees paid by the Borrower during
         such quarters) plus (h) for any calculation that includes any fiscal
         quarter or quarters ended during the fiscal year ending July 31, 2001,
         the actual amount of the extraordinary legal fees paid during such
         fiscal quarter or quarters; provided that the aggregate amount of the
         legal fees that may be added to the EBITDA calculation for the fiscal
         year ending July 31, 2001, shall not be greater than $350,000 plus (i)
         for any calculation that includes the fiscal quarter ending July 31,
         2000, $1,000,000 (which amount is the cash portion of the settlement
         described in Fourth Amendment Schedule 1 attached hereto)."

                  "'Fixed Charge Coverage Ratio' means, for any period, the
         ratio of (a) the sum of the following (without duplication) for the
         Borrower and its Subsidiaries for such period determined on a
         consolidated basis in accordance with GAAP: (i) Net Income, plus (ii)
         Interest Expense, plus (iii) income and franchise taxes to the extent
         deducted in determining Net Income, plus (iv) depreciation and
         amortization expense and other non-cash items to the extent deducted in
         determining Net Income, minus (v) non-cash income to the extent
         included in determining Net Income, plus (vi) Lease Expense, minus
         (vii) Capital Expenditures, plus (viii) for any calculations that
         include the fiscal quarter ended (A) October 31, 1999, $241,900, (B)
         January 31, 2000, $199,000, (C) April 30, 2000, $259,200, or (D) July
         31, 2000, $290,000 (which amounts referred to in this clause (viii)
         relate to extraordinary legal and accounting fees paid by the Borrower
         during such quarters) plus (ix) for any calculation that includes any
         fiscal quarter or quarters ended during the fiscal year ending July 31,


FOURTH AMENDMENT TO SECOND AMENDED AND RESTATED CREDIT
AGREEMENT - Page 4
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         2001, the actual amount of the extraordinary legal fees paid during
         such fiscal quarter or quarters; provided that the aggregate amount of
         the legal fees that may be added to the Fixed Charge Coverage Ratio
         calculation for the fiscal year ending July 31, 2001, shall not be
         greater than $350,000 plus (x) for any calculation that includes the
         fiscal quarter ending July 31, 2000, $1,000,000 (which amount is the
         cash portion of the settlement described in Fourth Amendment Schedule 1
         attached hereto) to (b) the Fixed Charges of the Borrower and its
         Subsidiaries for such period."

                  "'Interest Period' means, with respect to any Eurodollar Loan,
         each period commencing on the date such Loan is made or Converted from
         an ABR Loan or (if Continued) the last day of the next preceding
         Interest Period with respect to such Loan, and ending on the
         numerically corresponding day in the first calendar month thereafter,
         except that each such Interest Period which commences on the last
         Business Day of a calendar month (or on any day for which there is no
         numerically corresponding day in the subsequent calendar month) shall
         end on the last Business Day of the subsequent calendar month.
         Notwithstanding the foregoing: (a) each Interest Period which would
         otherwise end on a day which is not a Business Day shall end on the
         next succeeding Business Day (or, if such succeeding Business Day falls
         in the next succeeding calendar month, on the next preceding Business
         Day); (b) any Interest Period which would otherwise extend beyond the
         Maturity Date shall end on the Maturity Date; (c) no more than five
         Interest Periods for Eurodollar Loans shall be in effect at the same
         time; (d) no Interest Period shall have a duration of less than one
         month and, if the Interest Period for any Eurodollar Loans would
         otherwise be a shorter period, such Loans shall not be available
         hereunder; and (e) no Interest Period for a Loan may commence before
         and end after any principal repayment date unless, after giving effect
         thereto, the aggregate principal amount of the Eurodollar Loans having
         Interest Periods that end after such principal payment date shall be
         equal to or less than the amount of the applicable Loans scheduled to
         be outstanding hereunder after such principal payment date."

                  "'Maturity Date' means November 30, 2001."

                  "'Outstanding Credit' means, at any particular time, the sum
         of (a) the aggregate outstanding principal amount of the Loans plus (b)
         the Letter of Credit Liabilities."

                  "'Revolving Period Termination Date' means the Maturity Date."


FOURTH AMENDMENT TO SECOND AMENDED AND RESTATED CREDIT
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         (b) Addition of Definitions. Section 1.1 of the Credit Agreement is
hereby amended to add the following new terms and definitions, which shall
appear in alphabetical order in such Section 1.1:

                  "'Amortizing Loan Portion' means that portion of the principal
         amount of the Loans outstanding as of the Fourth Amendment Effective
         Date in an amount equal to $32,234,000."

                  "'Borrowing Base' means, at any date of determination, an
         amount equal to 80% of Eligible Receivables (in Dollars) of the
         Borrower and its Subsidiaries; provided, however, that, notwithstanding
         anything to the contrary contained in this Agreement, if any of the
         Agent or any Lender shall have received written notice from any Loan
         Party purportedly sent to terminate, limit or restrict (or to attempt
         to terminate, limit or restrict) future advances or future Obligations
         or the operation of any Security Document as security for future
         advances or future Obligations, whether or not such notice is
         effective, the Borrowing Base shall be further reduced by an amount
         equal to the aggregate value of the Eligible Receivables to which such
         notice relates, as such value is determined by the Agent in good
         faith."

                  "'Borrowing Base Report' means a report in substantially the
         form of Exhibit G attached hereto and completed and certified by a
         Responsible Officer of the Borrower relating to the determination of
         the Borrowing Base."

                  "'Eligible Receivables' means, at any date of determination,
         without duplication, the aggregate of each Receivable owned by the
         Borrower or any Subsidiary of the Borrower, created in the ordinary
         course of business which satisfies each of the following conditions:

                           (a) Such Receivable complies with all applicable
                  Governmental Requirements, including, without limitation to
                  the extent applicable, usury laws, the Federal Truth in
                  Lending Act and Regulation Z of the Board of Governors of the
                  Federal Reserve System and similar Canadian laws;

                           (b) Such Receivable, at the date of issuance of its
                  invoice, (i) was payable not more than 30 days after the
                  original date of issuance of the invoice therefor or (ii) was
                  payable more than 30 days and not more than 60 days after the
                  original date of issuance of the invoice therefor and was
                  payable by an account debtor and pursuant to terms approved by
                  the Agent in writing;


FOURTH AMENDMENT TO SECOND AMENDED AND RESTATED CREDIT
AGREEMENT - Page 6
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                           (c) Such Receivable has not been outstanding for more
                  than 60 days past the original date of invoice;

                           (d) Such Receivable represents a legal, valid and
                  binding payment obligation of the account debtor enforceable
                  in accordance with its terms and arising from an enforceable
                  contract, the performance of which contract, insofar as it
                  relates to such Receivable, has been completed by the Borrower
                  or one of its Subsidiaries (as applicable);

                           (e) Such Receivable does not arise from the sale of
                  any Inventory on a bill-and hold, guaranteed sale,
                  sale-or-return, sale on approval, consignment or any other
                  repurchase or return basis;

                           (f) The Borrower or one of its Subsidiaries (as
                  applicable) has good and indefeasible title to such
                  Receivable, the Agent holds a perfected first priority Lien on
                  such Receivable pursuant to the Security Documents (unless
                  such Receivable is owned by a Subsidiary organized under the
                  laws of Canada or a province thereof), and such Receivable is
                  not subject to any Liens except Liens in favor of the Agent
                  pursuant to the Loan Documents;

                           (g) Such Receivable does not arise out of a contract
                  with, or an order from, an account debtor that, by its terms
                  (other than terms which are invalid under applicable law),
                  prohibits or makes void or unenforceable the grant of a
                  security interest to the Agent in and to such Receivable;

                           (h) The amount of such Receivable included in
                  Eligible Receivables is not subject to any setoff,
                  counterclaim, defense, dispute, recoupment or adjustment other
                  than normal discounts for prompt payment offered in the
                  ordinary course of business, and control over collection of
                  such Receivable has not been contractually relinquished to an
                  attorney, collection agency or other third party;

                           (i) The account debtor with respect to such
                  Receivable is not (i) in the judgment of the Agent in the
                  exercise of its discretion in good faith, unable to pay such
                  Receivable due to such account debtor's financial condition or
                  performance and (ii) is not insolvent or the subject of any
                  bankruptcy or insolvency proceeding and has not made an
                  assignment for the benefit of creditors, suspended normal
                  business operations, dissolved,


FOURTH AMENDMENT TO SECOND AMENDED AND RESTATED CREDIT
AGREEMENT - Page 7
<PAGE>   8
                  liquidated, terminated its existence, ceased to pay its debts
                  as they become due or suffered a receiver or trustee to be
                  appointed for any of its assets or affairs;

                           (j) Such Receivable is not evidenced by chattel paper
                  or instruments unless the Lien on such chattel paper or
                  instrument is a perfected first priority Lien on such chattel
                  paper or instrument in favor of the Agent pursuant to the
                  Security Documents;

                           (k) The account debtor has not returned or refused to
                  retain, or otherwise notified such Borrower or any other Loan
                  Party of any dispute concerning, or claimed nonconformity of,
                  any of the Inventory or services relating to such Receivable;

                           (l) Such Receivable is not owed by an Affiliate of
                  any Borrower or one of its Subsidiaries (as applicable);

                           (m) Such Receivable is payable in Dollars or Cdn.
                  Dollars by the account debtor;

                           (n) The account debtor with respect to such
                  Receivable is not domiciled in or organized under the laws of
                  any country other than the U.S. or Canada;

                           (o) Such Receivable is not owed by an account debtor
                  as to which more than ten percent of the aggregate balances
                  then outstanding on all Receivables owed by such account
                  debtor thereon and/or its Affiliates to the Borrower or one of
                  its Subsidiaries (as applicable) are more than 90 days past
                  the original date of invoice; provided, that if a single
                  invoice causes the outstanding Receivables from an account
                  debtor that are 90 days past due to be greater than ten
                  percent of the aggregate Receivables owed by such account
                  debtor, but such Receivables from such invoice otherwise are
                  "Eligible Receivables" but for this clause (o) or clause (c)
                  of this definition, then only such Receivables from such
                  invoice will be excluded in determining "Eligible
                  Receivables";

                           (p) The account debtor with respect to such
                  Receivable is not the U.S. or any state thereof, Canada or any
                  province thereof or any department, agency or instrumentality
                  of any of the foregoing, unless, with respect to the Lien on
                  such Receivable in favor of the Agent, the Federal Assignment
                  of Claims Act of 1940, as amended, or the state equivalent
                  thereof (with respect to the


FOURTH AMENDMENT TO SECOND AMENDED AND RESTATED CREDIT
AGREEMENT - Page 8
<PAGE>   9
                  U.S. or any state thereof or any department, agency or
                  instrumentality thereof) or the Financial Administration Act
                  (Canada), as amended, or the Canadian provincial equivalent
                  thereof (with respect to Canada or any province thereof or any
                  department, agency or instrumentality thereof), as amended and
                  as may be applicable, shall have been complied with as the
                  same relates to such Receivable;

                           (q) The account debtor with respect to such
                  Receivable is not located in New Jersey, Minnesota, West
                  Virginia or any other state or province denying creditors
                  access to its courts in the absence of a notice of business
                  activities report or other similar filing, unless Borrower or
                  one of its Subsidiaries (as applicable) has either qualified
                  as a foreign corporation authorized to transact business in
                  such state or province or has filed a notice of business
                  activities report or similar appropriate filing with the
                  applicable state agency for the then-current year;

                           (r) Such Receivable is not owed by an account debtor
                  as to which the aggregate of all Receivables owing by such
                  account debtor or an Affiliate of such account debtor exceeds
                  ten percent of the aggregate of all Receivables at such date,
                  provided that an amount of Receivables owing by such account
                  debtor that do not exceed ten percent of the aggregate of all
                  Receivables at such date shall not be excluded pursuant to
                  this clause (r); and

                           (s) Such Receivable is not otherwise deemed
                  'ineligible' for borrowing purposes by the Agent in the
                  exercise of its reasonable discretion in good faith.

                           The amount of the Eligible Receivables owed by an
                  account debtor to the Borrower or one of its Subsidiaries (as
                  applicable) shall be net of, and shall be reduced by (if and
                  to the extent not already so reduced by virtue of the
                  preceding clauses of this definition), the amount of all
                  contra accounts, reserves, credits, rebates and (subject to
                  the proviso below) other indebtedness, liabilities or
                  obligations owed by the Borrower or one of its Subsidiaries
                  (as applicable) to such account debtor; provided, however,
                  that the existence of any such other indebtedness, liabilities
                  or obligations owed by such Borrower to such account debtor
                  shall not, in and of itself, reduce the amount of Eligible
                  Receivables owed by such account debtor by the amount of such
                  other indebtedness, liabilities or obligations (for purposes
                  of this sentence or clause (h) preceding of this definition)
                  except to the


FOURTH AMENDMENT TO SECOND AMENDED AND RESTATED CREDIT
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<PAGE>   10
                  extent that such other indebtedness, liabilities or
                  obligations are then due."

                  "'Excess Cash Flow' means, for any fiscal year, and without
         duplication, the positive remainder (if any) of (a) EBITDA for such
         fiscal year minus (b) the sum of (i) taxes payable by Borrower and its
         Subsidiaries in cash for such fiscal year, plus (ii) all principal and
         cash interest payments on Debt made by Borrower or its Subsidiaries
         during such fiscal year, whether optional, mandatory or scheduled
         payments, plus (iii) the lesser of (A) actual Capital Expenditures paid
         in cash during such fiscal year or (B) $4,000,000, minus (iv) any
         increase in working investment (i.e., the remainder of (A) the sum of
         Receivables plus "prepaids and other current assets" as set forth in
         the Borrower's financial statements delivered pursuant to Section 8.1)
         during such fiscal year, minus (B) "accounts payable and accrued
         liabilities" as set forth in the Borrower's financial statements
         delivered pursuant to Section 8.1), plus (v) any decrease in working
         investment (i.e., the remainder of (A) accounts payable and accrued
         liabilities minus (B) the sum of Receivables plus prepaids and other
         current assets) during such fiscal year."

                  "'Fourth Amendment Effective Date' means July 31, 2000."

                  "'Loans' means as specified in Section 2.1, and 'Loan' means
         any of such Loans. Without limiting the generality of the foregoing,
         the term 'Loans' includes both the Revolving Loan Portion and the
         Amortizing Loan Portion."

                  "'Monthly Date' means the last day of each month of each year,
         the first of which shall be October 31, 2000."

                  "'Reliance Letter of Credit' means the letter of credit in the
         face amount of $794,000 issued by Bank of America in favor of Reliance
         National as beneficiary for the account of the Borrower, which expires
         June 20, 2001."

                  "'Revolving Loan Portion' means (a) that portion of the
         principal of the Loans outstanding as of the Fourth Amendment Effective
         Date that is not a part of the Amortizing Loan Portion of the Loans and
         (b) any other Loans made on or after the Fourth Amendment Effective
         Date under Section 2.1(a)."

         (c) Amendment to Section 2.1(a). Section 2.1(a) of the Credit Agreement
is hereby amended and restated to read in its entirety as follows:


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                  (a) Loans. Subject to the terms and conditions of this
         Agreement (including, without limitation, Section 2.12), each Lender
         severally agrees to make one or more loans to the Borrower from time to
         time from and including the Closing Date to but excluding the Revolving
         Period Termination Date up to but not exceeding the positive remainder
         of (i) the amount of such Lender's Commitment as then in effect, minus
         (ii) such Lender's Commitment Percentage of the Letter of Credit
         Liabilities then outstanding. (The loans at any time made by any one or
         more of the Lenders to the Borrower pursuant to the Original Agreement,
         the Existing Agreement or this Agreement are herein collectively called
         the 'Loans'). Subject to the foregoing limitations and the other terms
         and conditions of this Agreement, the Borrower may borrow, repay and
         reborrow the Revolving Loan Portion of the Loans during (but not after)
         the Revolving Period; provided, however, that the aggregate amount of
         the outstanding Revolving Loan Portion of the Loans plus the Letter of
         Credit Liabilities shall not at any time exceed the Borrowing Base. The
         Borrower may not repay and reborrow the Amortizing Loan Portion of the
         Loans. The Borrowing Base shall be determined in good faith by the
         Agent as of the Fourth Amendment Effective Date and shall be
         redetermined in good faith by the Agent monthly thereafter concurrently
         with the delivery, or required date of delivery, of the Borrowing Base
         Report to be delivered in accordance with Section 8.1(e). In addition,
         the Borrowing Base may be redetermined at any time and from time to
         time by the Agent in good faith upon the occurrence and during the
         continuation of a Default."

         (d) Amendment to Section 2.3. Section 2.3 of the Credit Agreement is
hereby amended and restated to read in its entirety as follows:

                  "Section 2.3 Repayment of Loans. The Borrower shall pay to the
         Agent for the account of each applicable Lender the principal of the
         Loans (including the Amortizing Loan Portion of the Loans) outstanding
         as of the Maturity Date (and the principal of the Loans outstanding as
         of the Maturity Date shall be due and payable) in full on the Maturity
         Date. In addition to the foregoing, the Borrower shall pay to the Agent
         for the account of each applicable Lender the outstanding principal of
         the Amortizing Loan Portion of the Loans in eight installments, as
         follows:


<TABLE>
<CAPTION>
                             Payment Date                Payment Amount
                             ------------                --------------
<S>                       <C>                            <C>
                          November 15, 2000                 $794,000

                          January 31, 2001                  $875,000

                          April 30, 2001                    $875,000

                          July 31, 2001                     $875,000

                          October 31, 2001                $1,375,000
</TABLE>


FOURTH AMENDMENT TO SECOND AMENDED AND RESTATED CREDIT
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         (e) Amendment to Section 2.4. Section 2.4 of the Credit Agreement is
hereby amended and restated in its entirety to read as follows:

                  "Section 2.4 Interest.

                  (a) Interest Rate. The Borrower shall pay to the Agent for the
         account of each Lender interest on the unpaid principal amount of each
         Loan made by such Lender (or deemed made by such Lender with respect to
         a Loan assigned to such Lender after the making of such Loan) to the
         Borrower for the period commencing on the date of such Loan to but
         excluding the date such Loan shall be paid in full, at the following
         rates per annum:

                           (i) during the periods such Loan is an ABR Loan, the
                  lesser of (A) the ABR plus the Applicable Margin or (B) the
                  Maximum Rate; and

                           (ii) during the periods such Loan is a Eurodollar
                  Loan, the lesser of (A) the Eurodollar Rate plus the
                  Applicable Margin or (B) the Maximum Rate.

                  (b) Payment Dates. Accrued interest on the Loans shall be due
         and payable as follows:

                           (i) in the case of ABR Loans, on each Monthly Date;

                           (ii) in the case of each Eurodollar Loan, on the last
                  day of the Interest Period with respect thereto;

                           (iii) upon the payment or prepayment (whether
                  mandatory or optional) of any Loan or the Conversion of any
                  Loan to a Loan of the other Type (but only on the principal
                  amount so paid, prepaid or Converted); and

                           (iv) on the Maturity Date."

         (f) Amendment to Section 2.6. Section 2.6 of the Credit Agreement is
hereby amended by (i) deleting the phrase "(other than a Swingline Advance)" and
(ii) restating clause (d) to read as follows:

         "(d) optional prepayments of the Loans shall be applied first to the
         outstanding principal of the Revolving Loan Portion of the Loans and
         then to the installments due under the Amortizing Loan Portion of the
         Loans in the inverse order of the maturities of such installments."


FOURTH AMENDMENT TO SECOND AMENDED AND RESTATED CREDIT
AGREEMENT - Page 12
<PAGE>   13

         (g) Amendment to Section 2.7. Section 2.7 of the Credit Agreement is
hereby amended and restated in its entirety to read as follows:

                  "Section 2.7. Minimum Amounts. Except for Conversions and
         prepayments pursuant to Article 4, each borrowing, each Conversion and
         each prepayment of principal of the Loans shall be in an amount at
         least equal to $500,000 (borrowings, prepayments or Conversions of or
         into Loans of different Types or, in the case of Eurodollar Loans,
         having different Interest Periods at the same time hereunder shall be
         deemed separate borrowings, prepayments and Conversions for purposes of
         the foregoing, one for each Type or Interest Period)."

         (h) Amendment to Section 2.8. The entire portion of Section 2.8 of the
Credit Agreement immediately following the table contained in such section
(commencing with the sentence beginning with the phrase "Each such notice") is
hereby amended and restated in its entirety to read as follows:

         "Each such notice of termination or reduction shall specify the amount
         of the Commitments to be terminated or reduced. Each such notice of
         borrowing, Conversion, Continuation or prepayment shall specify the
         Loans to be borrowed, Converted, Continued or prepaid and the amount
         (subject to Section 2.7 hereof) and Type of the Loans to be borrowed,
         Converted, Continued or prepaid (and, in the case of a Conversion, the
         Type of Loans to result from such Conversion) and the date of
         borrowing, Conversion, Continuation or prepayment (which shall be a
         Business Day). Notices of borrowings, Conversions, Continuations or
         prepayments shall be in the form of Exhibit C hereto, appropriately
         completed as applicable. Each such notice which includes reference to
         the duration of an Interest Period shall specify the Loans to which
         such Interest Period is to relate. The Agent shall promptly notify the
         Lenders of the contents of each such notice. In the event the Borrower
         fails to select the Type of Loan within the time period and otherwise
         as provided in this Section 2.8, such Loan (if outstanding as a
         Eurodollar Loan) will be automatically Converted into an ABR Loan on
         the last day of the preceding Interest Period for such Loan or (if
         outstanding as an ABR Loan) will remain as, or (if not then
         outstanding) will be made as, an ABR Loan. The Borrower may not borrow
         any Eurodollar Loans, Convert any Loans into Eurodollar Loans or
         Continue any Loans as Eurodollar Loans if the interest rate for such
         Eurodollar Loans would exceed the Maximum Rate."


FOURTH AMENDMENT TO SECOND AMENDED AND RESTATED CREDIT
AGREEMENT - Page 13
<PAGE>   14
         (i) Amendment to Sections 2.10(a) and 2.12. Section 2.10(a) of the
Credit Agreement is hereby amended by deleting the last sentence thereof in its
entirety, and Section 2.12(a) of the Credit Agreement is hereby amended by
deleting clause (a) therein in its entirety.

         (j) Amendment to Section 2.13(a). Section 2.13(a) of the Credit
Agreement is hereby amended and restated in its entirety to read as follows:

                  "(a) Subject to the terms and conditions of this Agreement,
         the Borrower may utilize the Commitments by requesting that the Issuing
         Bank issue Letters of Credit; provided, that the aggregate amount of
         outstanding Letter of Credit Liabilities shall not at any time exceed
         $4,000,000. Upon the date of issue of each Letter of Credit, the
         Issuing Bank shall be deemed, without further action by any party
         hereto, to have sold to each Lender, and each Lender shall be deemed,
         without further action by any party hereto, to have purchased from the
         Issuing Bank, a participation to the extent of such Lender's Commitment
         Percentage in such Letter of Credit."

         (k) Addition of Section 2.14. The Credit Agreement is hereby amended to
add the following Section 2.14 to the end of Article 2 of the Credit Agreement.

                  "Section 2.14  Mandatory Prepayments; Excess Cash Flow.

                  (a) If at any time the sum of the aggregate outstanding
         principal amount of the Revolving Loan Portion of the Loans plus the
         Letter of Credit Liabilities exceeds an amount equal to the lesser of
         (i) the Borrowing Base or (ii) the Commitment at such time, within one
         Business Day immediately after each occurrence thereof the Borrower
         shall pay to the Agent the amount of such excess as a prepayment of the
         Revolving Loan Portion of the Loans.

                  (b) The Borrower shall on October 30, 2001, pay (or cause to
         be paid) to the Agent, as a prepayment of the Loans and other
         Obligations then outstanding, an aggregate amount equal to fifty
         percent (50%) of the Excess Cash Flow for the fiscal year ended July
         31, 2001.

                  (c) Prepayments from Asset Dispositions. The Borrower shall,
         within five (5) days of receipt of Net Proceeds related to an Asset
         Disposition prepay the outstanding Loans as of such date in an
         aggregate amount equal to the Net Proceeds of such Asset Disposition.
         For purposes of this Agreement the following terms shall have the
         following meanings:


FOURTH AMENDMENT TO SECOND AMENDED AND RESTATED CREDIT
AGREEMENT - Page 14
<PAGE>   15

                           "Asset Disposition" means the disposition whether by
                  sale, lease, transfer, loss, damage, destruction, condemnation
                  or otherwise of any assets of Borrower or any of its
                  Subsidiaries other than sales of assets permitted under
                  Section 9.8.

                           "Net Proceeds" means cash proceeds (including
                  casualty insurance proceeds paid with respect to damage to
                  property) received by any Borrower or any of the Subsidiaries
                  from any Asset Disposition (including payments under notes or
                  other debt securities received in connection with any Asset
                  Disposition and insurance proceeds and awards of
                  condemnation), net of (a) the costs of such sale, lease,
                  transfer or other disposition (including professional fees and
                  expenses and taxes attributable to such sale, lease or
                  transfer which are actually expected to be paid) and (b)
                  amounts applied to repayment of Debt (other than the
                  Obligations) secured by a Lien on the asset disposed.

                  (d) Prepayment from Securities Offerings. In the event that
         Borrower or any of its Subsidiaries issues any Securities (as defined
         below), no later than the third (3rd) Business Day following the date
         of receipt of the proceeds from any such issuance, the Borrower shall
         prepay the outstanding Loans in an amount equal to the proceeds of such
         issuance, net of underwriting discounts and commissions and other
         reasonable costs associated therewith. "Securities" means any stock,
         shares, options, warrants, voting trust certificates, or other
         instruments evidencing an ownership interest or a right to acquire an
         ownership interest in a Person or any bonds, debentures, notes or other
         evidences of indebtedness, secured or unsecured.

                  (e) Application of Prepayments. Each prepayment under this
         Section 2.14 shall be accompanied with accrued and unpaid interest on
         the amount prepaid to the date of prepayment and any amounts payable
         under Section 4.5(a) and shall first be applied to the installments of
         principal due under the Amortizing Loan Portion of the Loans in the
         inverse order of the maturities of such installments and, thereafter,
         to any outstanding Revolving Loan Portion of the Loans.

         (l) Amendment to Section 3.1. Section 3.1 of the Credit Agreement is
hereby amended by deleting in their entireties each of the two clauses that
begin "provided, however," and end "paid in full".

         (m) Amendment to Section 3.2. Section 3.2 of the Credit Agreement is
hereby amended to add the following language to the end of Section 3.2:


FOURTH AMENDMENT TO SECOND AMENDED AND RESTATED CREDIT
AGREEMENT - Page 15
<PAGE>   16

         "The principal amount of the Revolving Loan Portion and the Amortizing
         Loan Portion of the Loans outstanding as of the Fourth Amendment
         Effective Date shall be allocated to and held by the Lenders pro rata
         based upon the respective amounts of their Commitments."

         (n) Addition of Section 5.9. The Credit Agreement is hereby amended to
add the following Section 5.9 to the end of Article 5 of the Credit Agreement.

                  "Section 5.9 Release of Liens securing Reliance Letter of
         Credit. The Lenders hereby authorize the Agent to, concurrently with
         the Borrower's paying the principal payment of the Amortizing Loan
         Portion of the Loans on November 15, 2000, release its Liens affecting
         $794,000 in cash collateral securing the Letter of Credit Liabilities
         relating to the Reliance Letter of Credit which were previously granted
         by the Borrower. The Lenders hereby further authorize the Agent to
         execute and deliver and to file or record (or to allow or cause to be
         filed or recorded), as appropriate, such agreements, documents and
         instruments as Agent, in its sole discretion, shall deem necessary or
         appropriate to effectuate such release."

         (o) Amendment to Section 8.1(a). Section 8.1(a) of the Credit Agreement
is hereby amended and restated to read in its entirety as follows:

                  "(a) Annual Financial Statements. As soon as available, and in
         any event within 90 days after the end of each fiscal year of the
         Borrower, beginning with the fiscal year ending July 31, 2001, (i) a
         copy of the annual audit report of the Borrower and its consolidated
         Subsidiaries as of the end of and for such fiscal year then ended
         containing, on a consolidated basis and with unaudited consolidating
         schedules attached, balance sheets and statements of income, retained
         earnings and cash flow, in each case setting forth in comparative form
         the figures for the preceding fiscal year, all in reasonable detail and
         audited and certified by BDO Seidman, LLP or other independent
         certified public accountants of recognized standing acceptable to the
         Agent and containing no qualification thereto except as may be
         reasonably acceptable to the Agent, to the effect that such report has
         been prepared in accordance with GAAP and (ii) a certificate of such
         independent certified public accountants to the Agent confirming the
         calculations set forth in the officer's certificate referred to in
         Section 8.1(d) delivered concurrently therewith;"

         (p) Amendment to Section 8.1(e). Section 8.1(e) of the Credit Agreement
is hereby amended and restated to read in its entirety as follows:


FOURTH AMENDMENT TO SECOND AMENDED AND RESTATED CREDIT
AGREEMENT - Page 16
<PAGE>   17

                  "(e) Borrowing Base Reports and Agings. As soon as available
         and in any event within 20 days after the end of each month, and, in
         any event from time to time upon the request of the Agent or the
         Required Lenders, (i) a Borrowing Base Report duly completed and (ii)
         an aged trial balance of all then-existing Receivables and all
         then-existing accounts payable of the Borrower and its Subsidiaries;"

         (q) Amendment to Section 8.6. Section 8.6 of the Credit Agreement is
hereby amended and restated to read in its entirety as follows:

                  "Section 8.6 Inspection Rights. Each of the Loan Parties will,
         and will cause each of its Subsidiaries to, permit representatives and
         agents of the Agent and each Lender, during normal business hours and
         upon reasonable notice to the Borrower, to examine, copy and make
         extracts from its books and records, to visit and inspect its
         Properties and to discuss its business, operations and financial
         condition with its officers and independent certified public
         accountants. The Borrower will authorize its accountants in writing
         (with a copy to the Agent) to comply with this Section 8.6. The Agent
         or its representatives may, at any time and from time to time at the
         Borrower's expense, conduct field exams or other inspections to verify
         the Borrowing Base and for such other purposes as the Agent may
         reasonably request; provided, however, that, prior to the occurrence of
         a Default, no more than three such field exams during any fiscal year
         shall be at the Borrower's expense."

         (r) Amendment to Section 10.2. Section 10.2 of the Credit Agreement is
hereby amended and restated to read in its entirety as follows:

                  "Section 10.2 Minimum Net Worth. The Borrower and its
         consolidated Subsidiaries will (i) as of July 31, 2000, $59,000,000,
         (ii) at all times after July 31, 2000, until such date that the capital
         stock issued pursuant to the settlement described in Fourth Amendment
         Schedule 1 attached hereto is deemed "stockholder's equity" pursuant to
         GAAP, maintain Net Worth in an amount equal to or greater than
         $57,700,000 and (ii) at all times on and after the date that such
         capital stock is deemed "stockholders equity" pursuant to GAAP,
         maintain Net Worth in an amount equal to or greater than $59,000,000."

         (s) Amendment to Section 10.3. Section 10.3 of the Credit Agreement is
hereby amended and restated to read in its entirety as follows:

                  "Section 10.3 Minimum Fixed Charge Coverage Ratio. The
         Borrower and its consolidated Subsidiaries will not permit the Fixed
         Charge Coverage Ratio calculated as of the end of each fiscal quarter


FOURTH AMENDMENT TO SECOND AMENDED AND RESTATED CREDIT
AGREEMENT - Page 17
<PAGE>   18

         identified below and for the four fiscal quarters then ended to be less
         than the ratio set forth below for the applicable fiscal quarter end":

<TABLE>
<CAPTION>
                       FISCAL QUARTER ENDED                        MINIMUM RATIO
                       --------------------                        -------------
<S>                                                                <C>
              July 31, 2000, October 31, 2000 and                  1.10 to 1.00
              January 31, 2001

              April 30, 2001 and each fiscal quarter               1.00 to 1.00
              end thereafter
</TABLE>

         (t) Amendment to Section 10.4. Section 10.4 of the Credit Agreement is
hereby amended and restated to read in its entirety as follows:

                  "Section 10.4 Capital Expenditures. The Borrower and its
         Subsidiaries (a) will not permit the aggregate Capital Expenditures of
         the Borrower and its Subsidiaries during the period from February 1,
         1999 through and including January 31, 2000 (exclusive of any purchase
         or acquisition of Capital Stock or assets permitted by clause (ii) of
         Section 9.3) to exceed $3,500,000, (b) will not permit the aggregate
         Capital Expenditures of the Borrower and its Subsidiaries during any
         period of four consecutive fiscal quarters ended during the period from
         April 30, 2000 through and including July 31, 2000 (exclusive of any
         purchase or acquisition of Capital Stock or assets permitted by clause
         (ii) of Section 9.3) to exceed $3,000,000, and (c) will not permit the
         aggregate Capital Expenditures of the Borrower and its Subsidiaries
         during any period of four consecutive fiscal quarters ended on or after
         October 31, 2000 (exclusive of any purchase or acquisition of Capital
         Stock or assets permitted by clause (ii) of Section 9.3) to exceed
         $4,000,000."

         (u) Amendment to Section 13.11. Section 13.11 of the Credit Agreement
is hereby amended and restated in its entirety to read as follows:

                  "Section 13.11 Amendments. No amendment or waiver of any
         provision of this Agreement, the Notes or any other Loan Document to
         which any Loan Party is a party, nor any consent to any departure by
         such Loan Party therefrom, shall in any event be effective unless the
         same shall be agreed or consented to by the Required Lenders and the
         applicable Loan Party or Loan Parties in writing, and each such waiver
         or consent shall be effective only in the specific instance and for the
         specific purpose for which given; provided, however, that no amendment,
         waiver or consent shall, unless in writing and signed by all of the
         Lenders and the applicable Loan Party or Loan Parties, do any of the
         following: (a) increase the Commitments of the Lenders or subject the
         Lenders to any


FOURTH AMENDMENT TO SECOND AMENDED AND RESTATED CREDIT
AGREEMENT - Page 18
<PAGE>   19
         additional obligations; (b) reduce the principal of, or interest on,
         the Loans or any fees or other amounts payable hereunder; (c) postpone
         any date fixed for any payment (including, without limitation, any
         mandatory prepayment) of principal of, or interest on, the Loans or any
         fees or other amounts payable hereunder; (d) waive any of the
         conditions precedent specified in Article 6; (e) change the Commitment
         Percentages or the aggregate unpaid principal amount of the Loans or
         the number or interests of the Lenders which shall be required for the
         Lenders or any of them to take any action under this Agreement; (f)
         change any provision contained in Section 3.2, Section 9.13 or this
         Section 13.11 or modify the definition of "Borrowing Base", "Eligible
         Receivables" or "Required Lenders" contained in Section 1.1; or (g)
         except as expressly authorized by this Agreement, release any
         Collateral from any of the Liens created by the Security Documents or
         release any guaranty of all or any portion of the Obligations; and
         provided further, however, that no amendment, waiver or consent
         relating to Sections 12.1, 12.2, 12.3, 12.4 or 12.5 shall require the
         agreement of any Loan Party. Notwithstanding anything to the contrary
         contained in this Section 13.11, no amendment, waiver or consent shall
         be made with respect to Article 12 hereof without the prior written
         consent of the Agent."

         (v) Deletion of Section 13.26. Section 13.26 of the Credit Agreement is
hereby deleted in its entirety from the Credit Agreement.

         (w) Addition of Exhibit G. Exhibit G, as attached hereto as Fourth
Amendment Exhibit G, is added to the Credit Agreement.

         3. Conditions Precedent. The effectiveness of this Amendment is subject
to the satisfaction of each of the following conditions precedent, all of which
conditions precedent must be satisfied on or before October 30, 2000:

         (a) The Agent shall have received all of the following in form and
substance satisfactory to the Agent:

                  (i) Amendment Documents. This Amendment as executed by the
         parties hereto and any other agreement, document, instrument or
         certificate reasonably required by the Agent or the Lenders to be
         executed or delivered by the Borrower or any other Loan Party in
         connection with this Amendment, each duly executed by each of the
         parties thereto (collectively, the "Amendment Documents");

                  (ii) Resolutions. Resolutions of the Board of Directors of the
         Borrower and the other Loan Parties certified by its Secretary or an
         Assistant Secretary which authorize the execution, delivery and
         performance by the


FOURTH AMENDMENT TO SECOND AMENDED AND RESTATED CREDIT
AGREEMENT - Page 19
<PAGE>   20

         Borrower and the other Loan Parties of this Amendment and the other
         Amendment Documents to which the Borrower or such Loan Party is or is
         to be a party;

                  (iii) Extension Fee. The extension fee referred to in
         Paragraph 15 of this Amendment;

                  (iv) Fees, Costs and Expenses. All fees, costs and expenses
         (including, without limitation, attorneys' fees and expenses) incurred
         by the Agent incident to this Amendment or required to be paid in
         accordance with Section 13.1 of the Credit Agreement, to the extent
         incurred and submitted to the Borrower, shall have been paid in full by
         the Borrower; and

                  (v) Additional Information. The Agent shall have received such
         additional agreements, documents, instruments and information as the
         Agent or its legal counsel, Jenkens & Gilchrist, a Professional
         Corporation, may reasonably request to effect the transactions
         contemplated hereby;

         (b) The representations and warranties contained herein and in all
other Loan Documents, as amended hereby, shall be true and correct as of the
date hereof as if made again on and as of the date hereof (except if and to the
extent that such representations and warranties are or were expressly made only
as of another specific date);

         (c) All corporate proceedings taken in connection with this Amendment
and the other Amendment Documents, and all legal matters incident thereto, shall
be reasonably satisfactory to the Agent and its legal counsel, Jenkens &
Gilchrist, a Professional Corporation; and

         (d) No Default or Event of Default shall have occurred and be
continuing (after giving effect to this Amendment).

         4. Condition Subsequent. The effectiveness of this Amendment is subject
to the condition subsequent that the Borrower shall have delivered to the Agent
and the Lenders, on or before November 10, 2000, the annual audit report of the
Borrower and its consolidated Subsidiaries as of and for the fiscal year ended
July 31, 2000 and all other financial statements, reports, certificates and
other information required to be delivered in accordance with Section 8.1(a), in
each case strictly in accordance with and as required by Section 8.1(a). In the
event that the condition subsequent set forth in this Paragraph 4 has not been
fully and timely satisfied on or before November 10, 2000, this Amendment shall
be, ipso facto, null and void and of no force or effect.

         5. Representations and Warranties. Each of the Borrower and the other
Loan Parties hereby jointly and severally represent and warrant to, and agrees
with, the Agent and the Lenders that, as of the date of and after giving effect
to this Amendment, (a) the


FOURTH AMENDMENT TO SECOND AMENDED AND RESTATED CREDIT
AGREEMENT - Page 20
<PAGE>   21
execution, delivery and performance of this Amendment and any and all other
Amendment Documents executed and/or delivered in connection herewith have been
authorized by all requisite corporate action on the part of the Borrower and the
other Loan Parties and will not violate the Borrower's or any Loan Party's
corporate charter or bylaws; (b) the term Loan Documents as defined in the
Credit Agreement and as used in any of the Loan Documents includes, without
limitation, the Amendment Documents; (c) all representations and warranties set
forth in the Credit Agreement and in the Security Documents are true and correct
as if made again on and as of such date (except if and to the extent that such
representations and warranties were expressly made only as of another specific
date); (d) no Default or Event of Default has occurred and is continuing (after
giving effect to this Amendment); (e) the Credit Agreement, the Notes, the
Guaranties, the Security Documents and the other Loan Documents (as amended by
this Amendment) are and remain legal, valid, binding and enforceable obligations
of the Borrower and the other Loan Parties (as applicable) which are parties
thereto in accordance with their terms; and (f) Fourth Amendment Schedule 1
attached hereto contains an accurate and reasonably complete summary of the
present status of the shareholder litigation as to which the Borrower is
defendant.

         6. Governing Law. THIS AMENDMENT AND THE OTHER LOAN DOCUMENTS SHALL BE
GOVERNED BY, AND CONSTRUED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF TEXAS
(WITHOUT REGARD TO CONFLICTS OF LAWS PRINCIPLES) AND APPLICABLE LAWS OF THE U.S.

         7. Counterparts. This Amendment may be executed in any number of
counterparts, all of which when taken together shall constitute one agreement,
and any of the parties hereto may execute this Amendment by signing any such
counterpart.

         8. No Oral Agreements. THIS AMENDMENT, TOGETHER WITH THE CREDIT
AGREEMENT AND THE OTHER LOAN DOCUMENTS AS WRITTEN, REPRESENT THE FINAL
AGREEMENTS BETWEEN AND AMONG THE PARTIES HERETO AND MAY NOT BE CONTRADICTED BY
EVIDENCE OF PRIOR, CONTEMPORANEOUS OR SUBSEQUENT ORAL AGREEMENTS OF THE PARTIES.
THERE ARE NO UNWRITTEN ORAL AGREEMENTS BETWEEN (A) THE BORROWER OR ANY OTHER
LOAN PARTY AND (B) THE AGENT OR ANY LENDER.

         9. Agreement Remains in Effect; No Waiver. Except as expressly provided
herein, all terms and provisions of the Credit Agreement and the other the Loan
Documents shall remain unchanged and in full force and effect and are hereby
ratified and confirmed. No waiver by the Agent or any Lender of any Default or
Event of Default shall be deemed to be a waiver of any other Default or Event of
Default. No delay or omission by the Agent or any Lender in exercising any
power, right or remedy shall impair such power, right or remedy or be construed
as a waiver thereof or an


FOURTH AMENDMENT TO SECOND AMENDED AND RESTATED CREDIT
AGREEMENT - Page 21
<PAGE>   22
acquiescence therein, and no single or partial exercise of any such power, right
or remedy shall preclude other or further exercise thereof or the exercise of
any other power, right or remedy under the Agreement, the Loan Documents or
otherwise.

         10. Survival of Representations and Warranties. All representations and
warranties made in this Amendment or any other Loan Document shall survive the
execution and delivery of this Amendment and the other Loan Documents, and no
investigation by the Agent or any Lender or any closing shall affect the
representations and warranties or the right of the Agent and the Lenders to rely
upon such representations and warranties.

         11. Reference to Credit Agreement. This Amendment shall constitute a
Loan Document. Each of the Loan Documents, including the Credit Agreement, the
Amendment Documents and any and all other agreements, documents or instruments
now or hereafter executed and/or delivered pursuant to the terms hereof or
pursuant to the terms of the Credit Agreement as amended hereby, are (if and to
the extent necessary) hereby amended so that any reference in such Loan
Documents to the Credit Agreement shall mean a reference to the Credit Agreement
as amended hereby.

         12. Severability. Any provision of this Amendment held by a court of
competent jurisdiction to be invalid or unenforceable shall not impair or
invalidate the remainder of this Amendment and the effect thereof shall be
confined to the provision so held to be invalid or unenforceable.

         13. Successors and Assigns. This Amendment is binding upon and shall
inure to the benefit of the Agent, the Lenders, the Borrower and the other Loan
Parties and their respective successors and assigns; provided, however, that
neither the Borrower nor any of the other Loan Parties may assign or transfer
any of its rights or obligations hereunder without the prior written consent of
the Lenders.

         14. Headings. The headings, captions and arrangements used in this
Amendment are for convenience only and shall not affect the interpretation of
this Amendment.

         15. Extension Fee. The Borrower shall pay to the Agent, on or before
the Fourth Amendment Effective Date, an extension fee in the amount of $258,670,
which extension fee shall be divided pro rata amongst the Lenders based upon
their respective Commitments.

         16. Release. In consideration of the agreements of the Agent and the
Lenders set forth in this Amendment, each of the Borrower, the other Loan
Parties and all of Borrower's and the other Loan Parties' heirs, personal
representatives, predecessors, successors and assigns (the "Releasors") hereby
fully releases, remises and forever discharges the Agent, the Lenders and each
of their respective parents and each of their


FOURTH AMENDMENT TO SECOND AMENDED AND RESTATED CREDIT
AGREEMENT - Page 22
<PAGE>   23
other affiliates and predecessors, and each and every one of their past and
present officers, directors, agents, employees, servants, partners,
shareholders, attorneys and managers, and all of their respective heirs,
personal representatives, predecessors, successors and assigns (collectively,
the "Lender-Related Parties") for, from and against any and all claims, liens,
demands, causes of action, controversies, offsets, obligations, losses, damages
and liabilities of every kind and character whatsoever, including, without
limitation, any action, omission, misrepresentation or other basis of liability
founded either in tort, contract or equity and the duties arising thereunder
(collectively, the "Claims") that the Releasors, or any of them, has had in the
past, or now has, whether known or unknown, whether asserted or unasserted, by
reason of any matter, cause or thing set forth in, relating to or arising out
of, or in any way connected with or resulting from, the Obligations, the Loan
Documents or any real or personal property now or at any time securing the
Obligations. It is the express intent of the Agent, the Lenders and the
Releasors that the release and discharge set forth in this Paragraph 16 be
construed as broadly as possible in favor of the Lender-Related Parties so as to
foreclose forever the assertion by any of the Releasors of any Claims, as
defined above, against the Lender-Related Parties or any of them.

         17. Borrower, Agent and each of the Banks agrees that the aggregate
amount of each Bank's Loans included in the Amortizing Loan Portion of the Loans
is as follows: Bank of America, National Association $12,613,304.38; Fleet
National Bank $7,007,391.30; Bank Austria Creditanstalt Corporate Finance, Inc.
$4,204,434.78; The Bank of Nova Scotia $4,204,434.78; and Bank One, Texas, N.A.
$4,204,434.76.

         IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
executed and delivered by their duly authorized officers effective as of the day
and year first above written.

                                    THE BORROWER AND ITS SUBSIDIARIES:

                                    DYNAMEX INC.

                                    By:
                                         ------------------------------
                                    Name:
                                          -----------------------------
                                    Title:
                                          -----------------------------


                                    DYNAMEX OPERATIONS EAST, INC. (successor by
                                    merger to U.S.C. Management Systems, Inc.
                                    and Cannonball, Inc.)


                                    By:
                                         ------------------------------
                                    Name:
                                          -----------------------------
                                    Title:
                                          -----------------------------


FOURTH AMENDMENT TO SECOND AMENDED AND RESTATED CREDIT
AGREEMENT - Page 23
<PAGE>   24

                                    DYNAMEX OPERATIONS WEST, INC.

                                    By:
                                         ------------------------------
                                    Name:
                                          -----------------------------
                                    Title:
                                          -----------------------------


                                    ROAD RUNNER TRANSPORTATION, INC.

                                    By:
                                         ------------------------------
                                    Name:
                                          -----------------------------
                                    Title:
                                          -----------------------------


                                    NEW YORK DOCUMENT EXCHANGE
                                    CORPORATION

                                    By:
                                         ------------------------------
                                    Name:
                                          -----------------------------
                                    Title:
                                          -----------------------------


                                    DYNAMEX DEDICATED FLEET SERVICES, INC.

                                    By:
                                         ------------------------------
                                    Name:
                                          -----------------------------
                                    Title:
                                          -----------------------------


                                    DYNAMEX CANADA INC.

                                    By:
                                         ------------------------------
                                    Name:
                                          -----------------------------
                                    Title:
                                          -----------------------------


FOURTH AMENDMENT TO SECOND AMENDED AND RESTATED CREDIT
AGREEMENT - Page 24
<PAGE>   25

                                    THE AGENT AND A LENDER:

Commitment:  $7,630,434.80          BANK OF AMERICA, NATIONAL ASSOCIATION,
                                    individually and as the Agent


                                    By:
                                         ------------------------------
                                    Name:
                                          -----------------------------
                                    Title:
                                          -----------------------------


                                    THE CO-AGENTS AND LENDERS:

Commitment:  $4,239,130.43          FLEET NATIONAL BANK,
                                    individually and as a Co-Agent

                                    By:
                                         ------------------------------
                                    Name:
                                          -----------------------------
                                    Title:
                                          -----------------------------


Commitment:  $2,543,478.26          BANK AUSTRIA CREDITANSTALT
                                    CORPORATE FINANCE, INC.,
                                    individually and as a Co-Agent

                                    By:
                                         ------------------------------
                                    Name:
                                          -----------------------------
                                    Title:
                                          -----------------------------


                                    By:
                                         ------------------------------
                                    Name:
                                          -----------------------------
                                    Title:
                                          -----------------------------


                                    ADDITIONAL LENDERS:

Commitment:  $2,543,478.26          THE BANK OF NOVA SCOTIA

                                    By:
                                         ------------------------------
                                    Name:
                                          -----------------------------
                                    Title:
                                          -----------------------------


Commitment: $2,543,478.25           BANK ONE, TEXAS, N.A.

                                    By:
                                         ------------------------------
                                    Name:
                                          -----------------------------
                                    Title:
                                          -----------------------------


FOURTH AMENDMENT TO SECOND AMENDED AND RESTATED CREDIT
AGREEMENT - Page 25
<PAGE>   26



                           FOURTH AMENDMENT EXHIBIT G

                        Exhibit G to the Credit Agreement

                          Form of Borrowing Base Report




FORM OF BORROWING BASE REPORT - Solo Page
<PAGE>   27



                          FOURTH AMENDMENT SCHEDULE 1

                        Status of Shareholder Litigation




FOURTH AMENDMENT SCHEDULE 1 - Solo Page