Heats once and stops

I have a Whirlpool Estate Gas Dryer model# TGDS840PQ1, When I first turn it on it works fine, the glow igniter turns on and the gas starts and the dryer gets hot. After a few minutes the flame shuts off (I think because the dryer is hot enough), then a few minutes later the igniter turns back on but the gas is not released?? I have already replaced the Thermal Fuse and the Therostat???