Just bought an '01, I have had an '01 7.3 f250 before but it's been 5 years. I just want to know if I would really gain anything going from my stock 3" exhaust with no muffler or anything, to an aftermarket 4" with everything delete? Also since I won't be really pulling a lot with it, would I really gain much from going with a performance air filter in the stock box, against an entire cold air intake system? Thanks in advance.