Thanks Mustang. I'm of the same opinion that the O2 sensor shouldn't be able to tell a difference, but I've heard of folks having problems with these trucks after removing the cats.

As far as removing the cats go, South Carolina doesn't have vehicle inspections, so I'm not really worried about it. I have an 84 F-150 with a 302 and essentially the same exhaust setup, and man it sounds a hundred times better with no cats.