[Lonestar_5293692]

My kenmore gas dryer start working perfectly ... Heat is nice and even and there is no noise or any thing but after a period of 15 to 20 minutes heat goes of and the cycle ends with a cold and damped cloths ... I already change the fuse and termistors and thermostats located in the back of the dryer and also clean all ducts from any dirt and now looks clean like brand new .... If I wait another 20 minutes and start it again it works again for the same length of time but shuts the heat again .... What should I check now so it could be fix ....? tNX