The heat must have come from the cat.

The boots on the plug wires would probably last forever if we didn't change plugs.

I messed up a couple of wires trying to get them off plugs and had to replaced them. Now I spray the inside of the boot with HD silicon spray and they come off easily when I change plugs.

I never had an overheated exhaust system but I did notice an improvement in gas mileage after installing a new set of plug wires.