I also forgot to mention one thing, my cat has a rattle in it, and I'm positive its not a heatshield, because with it on a hoist, i banged on it, and i hear rattle rattle. I yanked on the shields, but, they were pretty stiff. If it would be partially plugged, wouldn't that be the key to my answer? Wouldn't a plugged cat make too much backpressure, and cause the EGR to be open at all times and throw me a P0402 code(EGR sys excessive flow)?