I just realized something (duh). I don't have an H pipe on my duals. I'm running modded OEM stainless manifolds which have had the restrictive AIR bungs removed, but I don't have an H pipe. I had assumed that the exhaust shop woulda installed one automatically, but they didn't. You don't suppose that this, coupled with manifolds instead of full-length headers as recommended by GM, is the reason for my rich mixture, do ya?