Ive had a few different exhaust on my GV
Im actually going to be selling a stainless mandrel bent 2.5" exhaust that has a magnaflow muffler vibrant ultra quiet res and small bottle resonator in the next month and im located in Belleville.
My first exhaust was a custom Y pipe that was 2.5" and I had removed the 3rd cat and ran a flow master muffler and 2.5" tubbing and it sounded like a V8 at idle. WOT sounded good also.
Im going to be building a Y pipe for my XL7 in the next few weeks and if the money is right I would build another set.
Look up my name I posted the header and exhaust builds years ago also some youtube vids.