I cut everything out after the 3rd "Cat" and replaced it with just pipes. It is slightly quieter than my 2008 Silverado with flowmaster super 40s. Kinda sad but these trucks are quiet.
I'm thinking next step is going to cut the 3rd "Cat" out, long tube and highflo cats but it might be too loud, anyone done this yet?
I was also thinking just doing the Long Tube Headers and keeping the stock cat, just have to relocate the existing cats to fit the header. I've done a lot of research and it's all over the place on how much HP gain Highflo is compared to the stock Cats.