Aleekat...thanks for the response. Yes, that is my suspicion.....motor drawing too much current. The fan does blow at all five speeds and the resistors appear to be in good shape. As I said, this is now the second time I've changed the switch. I noticed the temp buildup on the switch 'pin' ( when I remove the knob ) to verrrrry hot earlier this summer when I had the air conditioning on for periods of time. However, there didn't seem to be a similar problem over the winter when I had the blower on for heat.
Do you have any idea how many amps that blower motor should be drawing at high speed? I am thinking about using a clamp ammeter to check the amps. If they are high then I suspect it is the blower motor.
Also, could there be some HVAC filter of sorts that could be making the blower motor work harder?