I'm looking at Changing a few things on my 01, Biggest of all is starting with the Air Filter Unit to the Throttle body...What brands are out there as far as a good intake system for this truck goes, and What if anything can be done to increase the MPG that the Truck gets..?

It's got the 3.55's in the rear (I'd heard a sugguestion to replace those gears with the 3.73's is possible, but rather a HUGE headache) It has no muffler (Straight piped all the way back to the 6"
Tip) and I think that's about it...

Any ideas??