I have a 2005 Dodge std. cab cummins 2500 4X4 it's current mileage is 49,000 the original owner put a cat back system on it. I know the truck comes with a 4" from the turbo back is it more beneficial to step up to a 5" turbo back or just stick with the 4" and delete the cat? I have no idea what the muffler is... I was considering Diamond Eye. I had it on my 02 and loved the sound... For mods all I plan is a smarty jr, lift pump with air seperator, and intake... which leads me into my next question. On ebay I have seen a intake made by "Bills custom intakes" That looks like a great intake for the money and includes a S&B air filter for $179.00 seems like a smoken deal... Any advice. I would like to get away from the "perforated" inlet tube seems like it would create alot of disturbance in air flow??? Your guys' advice is greatly appriciated!!!