Well, from my experiance with my '99 SE V6, I battled with two dealers trying to get the cats replaced.
My last round was when they had my car for over a month trying to locate a intermintant problme, which turned out to be the PCM, done under warranty.
They did two O2 sensors aswell, and I had the other 2? done around a year prior under warranty aswell.
I said, considering the CEL codes kicking out pointed to the cats, and the car was acting like it had a plugged exhaust, the cats were bad.
then, at the last warranty trip the car had before the extented warranty expired, they said I needed all cats replaced, and darn it, 4K out of the federal warranty, and the quote I got, I about loaded my pants with the estimate.
I said, it was pretty conviant, they kept saying, no, cats are fine, they are fine, then 3 months later, they are all the sudden bad?
I still am holding a grudge over that.
I have been holding off, I have a set of manifolds I got from a fellow CEG'r, that I am going to install this summer. I should just do the msds headers with Mils and be done with it, but with my muscle car project, I'd rather just spend my fun time working on that instead.