in my SCrew with the 5.4 I was getting roughly 13-13.5 for a while -- now I get 15 pretty consistently. that's with the Air Force One, Gibson, and superchip. have about 12,000 mi right now. hoping it eventually crawls up and settles closer to 17, but i'm probably dreaming...

Wes

 

That is terrible. I can tell you that if I was only going to get 13mpg with one of these I would never have even thought about getting one. I guess that gas out there is really something. Or there would have to be something wrong with your truck. If there is not anything wrong with I would assume you would go through a set of spark plugs faster than the wrest of us.

 

dfwbmw,
Like I said before the truck runs fine but I do wonder if there's a problem ( a hole in the gas tank! haha) especially after reading some of these mileage claims.