I reused the gasket on mine. Just soak the bolts with a good penatrent, PB blaster, Aerokroil, for a couple of days before hand and take your time, pull the front pipe out of the exhaust and I also removed the bolts for the trans mount and jacked up the trans and engine to get the old one out. Took a little persuading to get the new one in. I noticed lower EGT's, deeper tone, and quicker cool down.
2003 2500HD LT CCLB, EFILive by Idaho Rob, 4" MBRP, Diamond Eye Down Pipe, Ported Intake Horn, S&B Intake, PPE Boost Valve, ADII, Nicktane CAT Adapter, CTS Insight, Cognito UCA, Rare Parts Tie Rods, Cognito Brace kit, Bilsteins, Gear Alloy wheels, Hankook RF10 285's, All on Mod, DDM 5k Low's & 4300 Fogs, air horn, on board air, limo tint, blue led interior