Just got it installed yesterday. Cat-back, single pipe, with a smaller muffler.
The dual tail pipes look great under the bumper. The sound isn't a real big change but the dual tail pipes really look awsome on the back.

Dealer's GM Supplier screwed up, and didn't order the dual wall angled tips I wanted, so the dealer instead, had the the single wall tips mounted and ordered me the correct pair. When they arrive tomarrow, I will pick them up and he said I could keep the single wall tips for free.