03/04 does not have a cat.I like the way mine runs with a 4 inch exhaust,AFE Stage 1 and the Rokktech sensor mod.If I had it to do over again I'd not go with the AFE Stage 1. I'd go with the factory box mod I see advertised that the intake air comes from floor of the box with a hose run near the front bumper and a good drop in filter.I can't get 1100 EGT hardly towing 10k on a 4 or 5 percent grade unless I really try .He's already has a Donaldson muffler.I'd finish the full four inch exhaust with a 4 inch downpipe from the back of the turbo and try a crank sensor mod,mod the air box and go from there.OPPS I noticed truck has a exhaust brake.That may stop a new four inch down pipe with out a new lower section of the exhaust brake.

 

03/04 can have a cat depending on where it is from. Florida did not require one. Intake and exhaust alone is not going to give much bang for the buck.

 

No but it lowers EGTs and with a crank sensor mod is a good place to start.Mine pulls anything I've hooked to it just fine and drives better then stock.When new the exhaust gave me a instant mpg increase.The intake system did not.The Rokktech sensor mod was a little but noticable improvement.