I'll throw in my statistics and ideas.
Im lifted a few inches and running 32s. I have run seafoam through the oil twice in the last year, and once through the pcv. I also changed my fuel filter less than a year ago, which I believe may have helped the mpg a bit. I have no added weight, and accelerate like a turtle just to improve mpg. Running Mobile 1 full synthetic oil. I typically average around 18 overall, about half city and half highway.
An interesting note (I have seen a few others on the forum mention this as well) - with 32s my mileage is perfectly accurate. I understand the simple theory that with bigger tires, you should be moving a greater distance than mileage indicates. However, when I compare my speedo to my Garmen gps, they are identical at every point. 20 mph on my speedo is 20 mph on the gps, and likewise at 75 mph, or any other speed. So my mpg calculations are accurate.
About two weeks ago I made the trip from my place in Wisconsin to my parents house in Wyoming for Christmas, and heres how it went:
- From my place all the way through Iowa I was averaging around 65 mph (except through a few towns), and got right around 19.5 mpg, which I think is pretty good. This was staying basically at the same elevation, with small ups and downs. No wind, and few downshifts.
- The next day I got into the God forsaken, insanely windy state called Nebraska. I was driving into the head winds with gusts around 50 (according to the radio), and going up in elevation (toward WY), driving at around 73 mph as the speed limit in NE is 75. With my cruise on the runner was downshifting into 4th and 3rd so much I thought it was gonna ruin my tranny. So I turned it off and just let myself slow down up hills and catch up some of the lost time going down hills. I hate when other people drive that way, but its the only way I could prevent the thing form downshifting every 10 seconds. Through NE I averaged 13.5 mpg!
So there are definately a number of variables that have a huge impact on mpg. With our wimpy engines, elevation and wind are BIG BIG factors, especially wind.
I remember last year driving back to WI after Christmas, with the wind pushing me, and going down in elevation at around 73 mph. My first 300 miles I averaged 22 mpg. And I fully expect the same mpg when I drive back later this week.
So if I made the drive this time at say 60 mph, going down in elevation, with tailwinds pushing me, I could see 23 mpg being a possibility. Though Ive never accomplished 23 in my truck thus far.
