Midnight,
You have a couple of options, a 2003/04 has a 3. 5 inch down pipe and intermediate pipe, then a 4. 0 tail pipe. Our MBRP MK96116 is technically designed for the 2004. 5+ trucks but will work on a 2003/04 if you are (1) willing to weld in extra material with a MIG welder to compensate for the 1/4er inch dimension difference where the MK96116 and the 3. 5 intermediate pipe join together or (2) get a 3. 5 to 4. 0 adaptor. Or you can get a complete MBRP or AFE system from the turbo out and just start all over. AFE also has a Tom Kat Kit that has a fairly long length of 4. 0 tubing that could replace the majority of your 3. 5 intermediate pipe for even better flow, costs less too.
Mark @ DPPI