I have achieved anywhere from an average of 13.0 mpg on a 26 gallon tank to 20.0 average. Depends on idle time, for example in the cold i let my truck run for a bit first, kills mpgs, the variation in city and hwy travel, tire psi, etc etc. In the fall seems to be the best mpg's for me..

Keep your foot out of it :p In the 4 years I've had my truck since it was brand new.. the best remedy i can find is keep her under 2k rpm on accleration and i set the cruise at 68 mph.. with my 3.21's.. im about 1450 rpm all day long on the highway.. BUT we also have very different trucks.. lol

The only way to get the best fuel mileage is to keep the engine tuned up, the oil changed, tire pressure on the high side of maximum and a light foot.