As far as the guy from California goes I’m surprised they didn’t impound your truck on the spot for modified exhaust as I thought anything different than what it had from the factory was a no go. If you haven’t replaced your injectors. I would get the GM equivalent and change them out. I would also see what the initial timing is set to and make sure it’s not bouncing as that can indicate a stretched timing chain. Unless you got a stock replacement cat none of the performance 1’s will do the same job the factory 1 did. And you really need to put it on a good scan tool to see what it’s doing and I would think that you’re going to have to go back to a stock exhaust setup so the po po stops harassing you