High Limit Safety Thermostat

Hello, My dryer is running fine, plenty of heat, but the timer is not moving and shutting off on the auto dry function. I haven't tried it on time dry or cotton settings yet. I am assuming it is the timer, which is fairly expensive. Is there any other part that may be leading to this problem other than the timer? I did have the dryer apart this summer to replace the belt. While it was open I cleaned it thoroughly. Vent pipe is clear and I regularly clean the vent screen. Thanks Bob