Whirlpool Dryer Shutting Off?

I have a Whirlpool Dryer "Model #LER7646EQ0". I am having a problem with it shutting off after approx. 5 minutes (it seems as if it is overheating). I have removed the blower wheel cover and cleaned it out. I will leave the dryer after it has shut off and it will start up the next day and then shut off again after it heats up or overheats. I have replaced the roller kit recently.
Is there a thermal switch that would do something like this? I am wondering if the motor has bearings that could go bad and is overheating? (or something like that) Is there a way to test the motor to see if it is OK? What other things do I need to check?
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Greg Nelson
August 2007