Talking about the TT cat-back system? They haven't offered the upper exhaust parts (dual downpipe) in years now, and that's the only part that gets you more HP. I've got a hi-flo cat and the TT cat-back, all 2" mandrel bent aluminized. I did not spring for the stainless borla muffler, just the standard dynomax. I like the sound. Throaty but subdued. Still kinda droney on the highway, but that's what my stereo is for
The TT kit includes everything you need, including NICE chain hangers and a new downpipe-to-cat gasket ring (a non-restrictive one to replace the fox restriction ring). Installs in an hour, tops.
I do need to have a test pipe made up soon, as the turbodiesel won't play nice with the gasser cat, and besides, next week is my last emissions test EVER.