I have a 2012 GMC Sierra 1500 with 2.75" exhaust pipe. I am wanting to delete my muffler and add a glasspack without welding. Problem is, I can't find any adapters to fit anything. Do I go with a 3" or a 2.5" glasspack? And whichever one I go with, what size adapters/reducers do I use? The muffler shops in this area charge around $350 for this work, so that's the reason for doing it myself. I appreciate any help given!!