Product review (5 stars): Worked perfectly to fix my whirlpool dryer!
If you like to take things apart and have a few hours of spare time to play around with some tools... keep reading.  If you are just not very handy, but don't want to pay much to try fixing your dryer, skip down to the bottom of my review.

After years of good service my Whirlpool Duet Gas Dryer (model GGW9200LW2) stopped heating properly.  The symptom I was experiencing was that even on high heat, the first minute or so of the cycle would heat up, but then it would fail to maintain temperature.  I had noticed over the last few months it seemed to take longer and longer to dry my laundry, usually taking several cycles to get the job done.

Having no knowledge of dryers, but enjoying attempting to fix things, I removed the back panel, top panel, and front lower panel which was not too much to deal with.  Basically there are about 15-20 screws you remove and it all just comes apart.  I was careful to label every screw I removed, keeping like parts in small jars so that I knew where things belonged when it came time to put it back together.  Once I was inside the dryer, I found a field diagnostic manual which outlined steps to diagnose issues, so I started by reading through that.

After a an hour with my multi-meter and following the directions from the manual, I hadn't found anything to be out of spec.  All of the continuity tests it suggested showed no issues.  To be completely thorough, I even went through the front electrical panel with all the buttons, using my multi-meter to verify all the buttons and knobs were functioning properly.  The procedure for troubleshooting the button panel was also clearly outlined in the manual, but took an additional 30 minutes and a second set of hands to hold the multi-meter probes while I pushed the proper buttons.  Long story short, I couldn't find anything wrong based on continuity, which is the easiest test to run, and I was getting frustrated.

I hit YouTube to look for a solution.  Most videos diagnosed the problem to be faulty solenoid valves based on the earlier described symptoms.  The valves had checked fine, but given they were only about $7, I figured it would be an easy starting point if I was going to replace parts.  Swapping the solenoids DID NOT fix the issue, so I moved on.  Looking over the manual again, I found a table which listed the proper exhaust temperature maximum for each dryer setting.  I had not checked this before, so I hooked the gas and power back up, then turned the dryer to the "normal" setting and fired it up.  I used my laser thermometer, aimed right into the exhaust port, and noted the highest temperature failed to ever reach the listed max temperature for the normal setting.  Again, to be thorough, I also checked the max temperature for the "high" setting-- which also topped out well under the listed max temperature.

Given the observation of the dryer failing to reach the correct temperatures in the table, it seemed logical to me that it might be the exhaust thermistor sensor.  Basically that's a fancy name for a tiny switch that cuts power when it gets hot.  I had originally ruled it out because my multi-meter conductivity test showed it was fine, but for only a few dollars, it was the obvious next step.  The part was in my hands 2 days later, it looked slightly different, but I swapped it out anyway because the screw holes lined up and BINGO!!! The dryer heated up to the correct temperature (as listed in the manual) and stayed there.  Problem solved.

If you have made it this far in the story, I have told you a long winded story outlining all the steps I took to fix my dryer from the perspective of a person who had NO IDEA WHAT THEY WERE DOING.  I am not a repair person so I just started taking things apart and guessing what might be the problem.  The thing is, the technology in a dryer really hasn't changed much since the 50's... so it can be pretty easy to fix if you are just willing to poke around a bit.

If your gas dryer is heating up initially, but failing to maintain temperature and you are a not very handy...DONT PANIC!  PUT DOWN THE PHONE...  Forget all the steps I took above and just do this:

~ buy both the solenoids & thermister for your model dryer.  Amazon has the handy tool which can even verify they fit your dryer by model number, but the parts I used are these:&nbsp;<a data-hook="product-link-linked" class="a-link-normal" href="/Supco-TH7274-Exhaust-Thermistor-Sensor/dp/B00SBWZIV0/ref=cm_cr_arp_d_rvw_txt?ie=UTF8">Supco TH7274 Exhaust Thermistor Sensor</a>&nbsp;&<a data-hook="product-link-linked" class="a-link-normal" href="/Whirlpool-279834-Valve-Coil-for-Dryer/dp/B004XLDEAU/ref=cm_cr_arp_d_rvw_txt?ie=UTF8">Whirlpool 279834 Valve Coil for Dryer</a>
~ unplug the dryer
~ open ONLY the front panel by removing the two small screws found at the lower corners on the face of the machine.  If you have the pedestal like I do, you need to open the drawer to expose them.
~ once you have the panel off, both parts will be right there in your face so they are easy to replace.
~ It should be obvious from looking at them, but you will need to remove a couple of small screws and transfer the electrical connectors from the old part to the new part.  TRANSFER THEM ONE AT A TIME! Do not just unplug everything and go for it.  Take one plug off and transfer it to the new part in the same place, then move onto the next.  I don't think polarity matters for these three parts, but just do it anyway, because it would be a really stupid way to find out I am wrong.
~ If swapping out those simple parts doesn't fix the issue, THEN you can start taking other things apart or call a repair service.  There is a better than 50/50 shot those parts are the culprit. Its worth the $15 dollars because the first thing the repair person will do is check/replace those anyway...of course after charging you $100-150 for the house call.

If you are going to attempt this yourself, feel free to ask me questions.  I am a very active reviewer and I always respond to comments.  Good luck!