Roper gas dryer starts up fine then runs cold for ever has new thermal fuse. Is 2 yr old

Take lint trap completely apart and clean and take exhaust hose off and clean it too. The dryer has a safety feature that won't allow overheating. Its like a car if it can't breath it won't run.

I just answered this question although I am not an expert but had same kind of problem so my answer might work or not at this point its worth a shot.

It's not how old it is, but how many loads of clothes have been through it. Each load puts a lining of concrete-hard lint deposits on all surfaces. You will have to take it apart and test the thermal fuse near the burner. You will have to clean the drier out thoroughly or it is all for nothing. Every air duct will have to be removed and scraped and washed out to remove baked on lint deposits which is like a concrete lining. This will burn so the manufacturer has installed the safeties to keep from having a house fire. The safeties are oval-shaped with a round center part containing the safety with two plug-on terminals for the wires and when they burn open from the dryer being dirty nothing will work. Using an ohm meter you put a lead on each terminal of the safety with wires unplugged and if it's good you will have a reading of about zero; if it's bad it will read infinity. Driers were the number one cause of fires at one time, hence now we have safety fuses. Look at: How to clean your clothes dryer. How to make it hot again. - YouTube (http://www.youtube.com/watch?v=MMP7BW1lLs4) to see how. Also: Mr. Appliance Tips: How to Clean Your Dryer - YouTube (http://www.youtube.com/watch?v=iBiRw-KElC4) ; Cleaning a Dryer Vent and Lint Trap - YouTube (http://www.youtube.com/watch?v=yFTZGgVisCI)
Electric Clothes Dryers (http://www.electrical-forensics.com/Dryer/ElectricClothesDryers.html)
Whirlpool Dryer Model LE5800XSW3 Wiring Diagram | Dryer Repair | Fixitnow.com Samurai Appliance Repair Man (http://fixitnow.com/wp/2010/10/09/whirlpool-dryer-model-le5800xsw3-wiring-diagram/)
When you finish cleaning the drier and install a new safety it is best to also replace the belt, too, because you do not want to have to disassemble it all over again and if the belt is over two years old you should replace it.

Note that on most of the videos it does not show them washing out the parts, but this is important because it's the only way to really get the parts clean, just don't get motor wet or the capacitor if it has one. Vacuum out the motor. I would move the drier out to your garage to have plenty of space to work. You also want to check your vent and clean it, also. The vent should have a short run and be straight as possible. The job is really easier than it sounds. There is no shortcut that will work; it has to be cleaned well. Before you re-assemble it make sure to use white lithium grease (high-temp grease) and grease all bearings. Just vacuuming out the dryer a little does little good. How well was it cleaned last time? If you do not wash out the parts dirt builds up faster. DrTom4444