Gas dryer starts warm, then blows cool air.?

I have a roper gas dryer. The ignitor (brand new) lights up, gas ignites and it blows hot air for a few minutes. Then it runs cold air for the rest of the cycle (which lasts forever because I don't think the timer works either). The thermal fuse tested 0 Ohms. Lint trap and vent pipe are unobstructed. I'm not sure which is my next part to replace on this hunk of junk to fix it.