When I was breaking in a cam on a V-6 S-10, I swapped 2 spark plug wires but drove it that way for a half hour and then saw the glowing red hot catalytic converter. Boy did it have some major power, after hollowing that out! So, if you drive it long and fast enough in the dark, you can see if a cat is glowing if you can stop fast enough and get out and look. If it is getting *that* hot....
Rob in AZ