You have bad gas coils.the coils on top of the gas valve need to be replaced,when they are failing,they will work fine until they heat up and then they shut down,when they cool down they will work for a while until they heat up again,the part number is 12001349 and they are around 45 bucks for the both of them,take out the two phillips screws, remove the cover,remove the wire connector do one coil at a time,also the coil with three wires has a metal spacer that stays on the post it slides down onto,sometimes it gets stuck inside the coil you're removing,if it's inside the old coil remove it and slide it back on the post and then slide the new coil down onto the post and plug your wires back on,put the cover back on and the two screws.push on the wire connectors to make sure they pushed on tight and your down.while your in the dryer if you haven't cleaned it out now is a good time to do so,this should be down once a year moreso with gas so you don't have a fire,vac out the dryer,if you have a shop vac put it on blow and blow the motor off and blow out the gas tube where the fire lights,remove and clean out the duct that the lint filter slides into and clean out the vent line and the outside vent,if it's a long run from the dryer to the outside i use a leaf blower to blow out the vent line,if you do this your clothes will dry on time,and it will be more energy efficient,the motor and other parts will last longer,if you need anymore help let me know,good luck