Also, the truck has had a custom dual exhaust that connects to an x pipe for equalization. There is no catalytic converter, as far as I can tell. Same headers and exhaust for the last 100k. I just wanted to let everyone know, to eliminate the catalytic converter as a suspected culprit.

I will climb under and take pictures of the entire exhaust system is anyone needs them. The x pipe (the place where the pipes come together before branching back out into dual pipes) has a heat shield on it.