I have the gibson axle back exhaust for close to a year now on my 15 altitude. It gives it a nice rumble when u get on it. Get the stainless steel one. I also put two magnaflows and got rid of the suitcase muffler so now this thing is louddd
So the suitcase is gone and two short magnaflows have replaced the suitcase. I have two dual straights for the 3.6 now and kept the stick reso's. The sound is quiet maybe a bit deeper. I asked them about an x-pipe and Lou's custom said it was not needed. It moves along good, about the same as before. Again not sure what an X or H pipe would give it different.
I don't know if I should get a retune from hemifever
From what i have heard the ;Borla Touring Cat-Back Exhaust Systems 140406 should fit direct bolt on, however you will need to change the rear deffer.. Summit racing has a review also on it. I will be getting it to see for myself