The cat is a Magnaflow hi-flow that I installed about 50k miles ago (it's a 49-state truck with only one cat), and the wideband is an Innovate Motorsports AFR gauge (plumbed into the exhaust tube, just upstream from the first O2 sensor).

I'm taking it into my tuning guy this week to get my muffler replaced (my old Flowmaster is finally falling apart - thank God! Getting a Magnaflow!), so hopefully we can nail down what the issue is. My wishful thinking is hoping that the muffler is so deteriorated that it's backing up the exhaust and causing the truck to run all screwy, but I know that's a long shot! Haha!

Thanks for your two cents, Greg. Always appreciated.