Well fueled the truck today and went 308 miles took 20 gallons and i got 15.4 mpg. Thats probably 85-90% highway only going 63 mph. Side note. My garmin says I went 322 miles so that would make it 16.1 mpg. Better yes but still think it should be better. Maybe it will take some time for the ECM to adjust, IDK? And my garmin is always the same as my calculations when used with our other vehicle. So why the difference? I've got stock wheels and tires and dual exhaust and no lift, fresh alignment and zero weight in the truck. And I drive like there is an egg under the foot pedal. My speedometer matches what the speed reads on the garmin so why 14 mile difference?

Well if anybody is reading this some input is sure welcomed.