07 VortecMax Sierra

I am looking for a "Factory" cat-back dual outlet exhaust system for my 07 Sierra with the 6.0 VMax package.

I thought I saw one in GM Performance Parts but cannot find it. I am looking to add the exhaust, intake & programmer to see if I can get over 400 HP out of this thing... It runs pretty good now but could do better & may get a 1 or 2 MPG better.... I do a lot of highway driving @ 75 or above...

Anyone know who makes the best exhaust system for the 6.0 ???

Thanks,

Supergas