Problem with 2000 White Outdoor LT1850 yard tractor electonic PTO?

My PTO switch turns the mower deck on/off fine for the first several minutes of use, but if I turn the PTO OFF after the mower has been running for 30 minutes or so, I cannot turn the PTO on again until the tractor has been off long enough to cool off, about 1/2 hour. Therefore I suspect the problem is heat-related, and not just the switch. What can you suggest?