I've heard the same claims...can't honestly say. I've been pretty shocked at how poor the mileage was with this truck as the one I had just before was identical except for the final drive...3.42 rather than 3.23...and the crushed front end against the I-12 retaining wall.
My initial highway mileage was 17 whereas the other was 20...not towing. Now I get as good as 21, but that's after all the stuff done to it. I can say, from experience, that the K&N and the Corsa Exhaust will pay for themselves...much sooner with gas like it is.

One thing's for certain...the thing will haul a$$ when you punch it!