Hey Im a first time diesel truck owner. I just bought an 04 GMC crew-cab, 4x4, LLY duramax. It has a "2" as the 8th digit in the VIN. Ive done alot of research on diesels, thats why I bought a duramax, plus Im a pretty big GM fan anyway. Now! I want to do a 4in exhaust right off the turbo, can I run my truck with out the CAT ? What kinda of gains on torque and MPG can I expect from this? How much with the cold-air and programmer. Got any suggestions on paticular bands?