I know I'm new here, but I wouldn't buy one for mpg increases; not worth it. I originally wanted the same thing until I did the math.
Lets say you currently avg. 17 mpg mixed driving. With Snow Performance's MPG MAX kit ($999) the claim is 10-15% increase. That's a 1.7-2.55 increase...= 74 miles.....= 3.79 gallons for a savings of $12.87 per tank. Thats 77.5 tanks to pay for it. It would take me 3.5 years to realize the savings. + the price of distilled water and methanol.
I bought mine from cooling mist, now for the EGT drop, around 150-250 depending on conditions, and a little power
Of course I don't have it installed yet, just thought I would offer my thoughts.
I think it depends on the truck as much as the driver anymore. I have a mild tune on mine (head bolt safe) and if I drive it my way, 10-12 C/H..... Driving with my kids, 14-16 C/H. Last road trip, 1,100 mi. roundtrip, I avg. 19 with cruise set at 78. Thats with a tuner, stock exhaust no muff, and tires at 65psi. Oh, and I run Optilube summer blend.
I'm sure I have read that if you take it to the dealer for work and they upload the latest flash it screws things up. The older flashes seemed to put out better mpg. Course I may be talking out of my arse. It just seems that I remember something to that effect. My truck hasn't seen a dealership for service since '08 I think, so maybe I have an older flash????