I just bought an 04 3500 and the guys I bought it from have no idea what has been done as far as upgrades or anything. It has a 5" pipe all the way through. Is that normal or an upgrade? It has an exhaust and would it be louder if I took that out and just continued that 5" pipe?

 

Got any pictures? 5" is not stock, and 2007.5 was the first year for the new SCR, with the DPF catalyst systems.
welcome to Diesel Bombers

 

4" is stock- is it straight piped? Should have a catalytic converter behind the turbo then muffler near the rear axle. Straight back = more air flow= happy easy breathing motor!