The only problem is they welded them where the old ones were. I got longer tips for a reason and they still put them in the same place
If I take them back to the shop is it gonna cost me anything to get them rewelded?
Yes the tips on the GT are long. How far do they stick out. If they are stainless you could cut them. If they are chrome you are stuck unless you get new tips. as far as the size of pipes are you going to do any engine mods like P&P heads, intakes and cam because if you are just leave the tailpipes alone. Even 2.5 is large for stock 3.8 motors you are really not going to notice much if any loss.