Here are your parts
Replacement parts for WHIRLPOOL REX5634PQ0 29" ELECTRIC DRYER | AppliancePartsPros.com
See the attachment for the tech sheet.
Is the timer advancing?
If it is not advancing does it not advance in both timed dry and auto modes?
If it does not advance in timed dry then odds are the timer is the problem.
If it advances in timed dry but not in auto mode then it could be a grounded element. If the element is grounded it can run all the time and the thermostats cannot shut it off.
This is important because 9in auto the timer motor gets power through the heating coil when it is turned off.
Check the heating coil.
Unplug the unit and both wires to the coil.
Check it with a meter, should be around 10 to 12 ohms.
Then check from each side of the coil to the case/frame, both should be infinite ohms (open). If not the coil may have sagged or broken and is touching the case.
Often you can see this.