well, i think the pipe going into the muffler is 2.75". then the dual i/o muffler with 2.75" goingto an y-pipe and then exiting with a 3.5" pipe.

so i'm thinking of using the 3=>2.5 muffler. it should easily weld onto the stock pipes. then have some new 2.5" pipes bent.

i think the stock system is similar to the Silverado SS and VHO trucks. this is one of the new vortec max's.