I've got my cutouts right after my y-pipe. When open, I loose a little low end, but I pick up power on the upper end. I wouldn't go 3'' true duals. On a 5.3L, I would go 2.5'' true duals...the x-pipe will negate the true dual setup, and the crossover should make it sounds a little crisper...an H-pipe can be also used, and it will make it sound a lot more throaty... An x-pipe is more of a performance crossover than an H-pipe.