I have to partially disagree. I say partially because I haven't done it to my truck yet but it will be happening in the next couple of months. (first will be the URD
True CAI next week, then exhaust of some kind next month) Soooo. my disagreement argument is that the engine is an air pump (some will say air / fuel pump) Either way an engine uses some of the energy is produces to move that air in and out or through the engine. So if you decrease the resistance, or drag on that air movement you decrease the energy used by the engine to pump it. Now in theory this should leave more power to go the wheels and therefor reduce the amount of fuel you need to deliver to maintain or gain the same speed. Increased efficiency increases MPG. The problem is that increased efficiency also give more "available" accessible power however small that may be, and we all (ok maybe just me) like the sound and feel of that power and we use the shit out of it. so we end up not seeing any increased mileage usually. driving habits will the be the biggest factor as to if you can not rape that extra power and leave it for the increased mileage.
now that all being said, it doesn't do a whole lot (but still a little) if you only open up one or the other, the intake or the exhaust. They need to both be done and done modestly for a V6 compared to a high displacement V8 to retain some back pressure needed in these new I-robot freaking engines.
whew. I'm tired now