[Big Platinum]

I have to agree with PC and Titan Augie, I've seen a good increase in mileage so far with my mods. The myth that MPG doesn't increase (or even goes down) with simple bolt-ons is due to the fact that most people will drive more aggresively with their new found power and sound. And yes, the tailgate method and tonneu cover will improve your highway mileage (and a little around town), this has been known for years.

The most important factor is driving style. It becomes more noticeable as the weight and power goes up. In a Honda Civic you can hardly see any difference in gas mileage according to how you drive it, start throwing around some weight and a healthy V8 and it becomes the primary contributing factor.