Exhibit 10.55

AMENDMENT TO MASTER TRUST AGREEMENT

THIS AMENDMENT to the Master Trust Agreement (“Master Trust”) is entered into
effective as provided herein below, between DYNEGY INC., an Illinois corporation
(“Dynegy Illinois”) and VANGUARD FIDUCIARY TRUST COMPANY, a trust company
incorporated under Chapter 10 of the Pennsylvania Banking Code (the “Master
Trustee”);

WITNESSETH

WHEREAS, Dynegy Illinois and certain subsidiaries and affiliated entities have
heretofore established the Dynegy Inc. 401(k) Savings Plan, the Dynegy Midwest
Generation, Inc. 401(k) Savings Plan for Employees Covered Under a Collective
Bargaining Agreement, the Dynegy Midwest Generation, Inc. 401(k) Savings Plan,
the Dynegy Northeast Generation, Inc. Savings Incentive Plan and the Extant,
Inc. 401(k) Plan (each such plan to referred to individually as “Plan” and
collectively as “Participating Plans”);

WHEREAS, Dynegy Illinois has entered into that certain Plan of Merger,
Contribution and Sale Agreement by and among Dynegy Illinois, LSP GEN Investors,
L.P., LS Power Partners, L.P., LS Power Equity Partners PIE I, L.P., LS Power
Equity Partners, L.P., LS Power Associates, L.P., Falcon Merger Sub Co., and
Dynegy Acquisition, Inc., executed September 14, 2006 (the “Merger Agreement”);

WHEREAS, pursuant to the transactions contemplated in the Merger Agreement,
Dynegy Illinois will become a wholly-owned subsidiary of a newly formed Delaware
corporation, named “Dynegy Inc.”, and Dynegy Illinois will thereafter be renamed
“Dynegy Illinois Inc.”, as of the Effective Time specified in the Merger
Agreement (the “Effective Time”);

WHEREAS, effective immediately after the Effective Time, Dynegy Illinois will
withdraw as the sponsor of the Participating Plans and Dynegy Inc., a Delaware
corporation, will assume sponsorship of the Participating Plans from Dynegy
Illinois and will become the “Employer” for purposes of the Master Trust; and

WHEREAS, pursuant to Article X of the Master Trust, Dynegy Illinois may amend
the Master Trust by delivery of an instrument in writing to the Master Trustee;

NOW, THEREFORE, BE IT RESOLVED that the Master Trust shall be, and hereby is
amended to provide that as follows, effective immediately after the Effective
Time:

1. The first paragraph of the Master Trust shall be deleted and the following
four paragraphs shall be substituted therefor:

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“THIS AGREEMENT OF TRUST (the ‘Agreement’) effective as of the 1st day of
January, 2002, by and between DYNEGY INC., an Illinois corporation (‘Dynegy
Illinois’) and VANGUARD FIDUCIARY TRUST COMPANY, a trust company incorporated
under Chapter 10 of the Pennsylvania Banking Code (the ‘Master Trustee’).

Dynegy Illinois has entered into that certain Plan of Merger, Contribution and
Sale Agreement by and among Dynegy Illinois, LSP GEN Investors, L.P., LS Power
Partners, L.P., LS Power Equity Partners PIE I, L.P., LS Power Equity Partners,
L.P., LS Power Associates, L.P., Falcon Merger Sub Co., and Dynegy Acquisition,
Inc., executed September 14, 2006 (the ‘Merger Agreement’).

Pursuant to the transactions contemplated in the Merger Agreement, Dynegy
Illinois will become a wholly-owned subsidiary of a newly formed Delaware
corporation, named ‘Dynegy Inc.’, and Dynegy Illinois will thereafter be renamed
‘Dynegy Illinois Inc.’, as of the Effective Time specified in the Merger
Agreement (the ‘Effective Time’).

Effective immediately after the Effective Time, Dynegy Illinois will withdraw as
the sponsor of the Participating Plans (defined below) and Dynegy Inc., a
Delaware corporation, will assume sponsorship of the Participating Plans from
Dynegy Illinois and all references to the ‘Employer’ in the Master Trust shall
thereafter refer to Dynegy Inc., a Delaware corporation.”

2. All references to “Company Stock” in the Master Trust shall refer to shares
of common stock of Dynegy Inc., a Delaware corporation.

3. All references to the “Dynegy Stock Fund” in the Master Trust shall refer to
the investment fund established and maintained to invest in common stock of
Dynegy Inc., a Delaware corporation.

4. Except as modified herein, the Master Trust shall remain in full force and
effect.

This Amendment may be executed in two or more counterparts, which together
constitute one instrument.

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IN WITNESS WHEREOF, the parties hereto have executed this Amendment to the
Master Trust on the dates indicated below, to be effective immediately after the
Effective Time.

 

Attest:     Dynegy Inc., an Illinois corporation       By:  

/s/ J. Kevin Blodgett

/s/ Irma Longoria

            Title:   Executive Vice President,         Administration      
Date:   April 2, 2007 Attest:     Vanguard Fiduciary Trust Company       By:  

 

      Title:  

 

      Date:  

 

      Approved and accepted: Attest:     Dynegy Inc., a Delaware corporation    
  By:  

/s/ J. Kevin Blodgett

/s/ Irma Longoria

            Title:   Executive Vice President,         Administration      
Date:   April 2, 2007