Hi this is Bryan, You may have one of a couple of problems, First check your dryer vent real good and make sure its blowing outside really strong.
Second you may have a bad thermostat, And third you may need gas valve coils. The best way to check if its a vent problem if your vent is hard to check,(to high off ground or goes through wall and cant clear) remove vent from dryer and see it it gets hot then. Is there a little plastic snap in cover about 1"x1" one the front of dryer you can pop off with a screwdriver? If there is this is for watching the flames in burner take it off and watch flame if there is one. the other tests are a little more difficult and require volt meter but do others first
Before checking your response today (I did it late last night and 4got) I came home and pulled out the dryer to remove the vent and tryed to clean it out with a dryer snake. Did not seem too dirty. i could not get the vent back on so husband came home while I was out and took his air compressor and "blew out" the vent and attached the vent back to the dryer.
I came home to the biggest mess you can imagine but the dryer is blowing much stronger outside than I ever remember. Dryer got very hot when I 1st turned it on but is already cold again. I have no snap cover on the front.