With the exception of about a month or so, I hand calc all my mileage every fillup. Gives me a heads up if numbers start trending down that something needs done. Most likely clean the MAF.

Got the truck in Feb with 132k on the clock, just turned 152k this past week. (yeah, that's 20k in six months. My gas bill is outrageous.) When I first got it my MAF was dirty, got around 9mpg. Still an improvement over the 7-8 I was getting with the old 78 with a 400. Cleaned the MAF in the middle of a road trip and immediately got 2 more mpgs. That was all with winter gas. Got a pretty steady 10.5 to 11.5 with my mix of highway and city.

Stopped calc for about a month and the switch was made to summer gas by the time I started keeping track again. Been a pretty steady 11.5 to 12.5 depending on how hard I try to keep the numbers up by not putting my foot down. Best was over 13 while I was doing a 70 mile or so commute each way for a week, all highway, and not driving job to job during the day.

Keep in mind my bed is full of tools and whatever crap I have collected that I haven't gotten motivated to take out yet. Like a piece of railroad to make an anvil out of. Prob 600+lbs of tools and such adding to the mass.

I've got the 285/75/r16 BFG AT kos and the only mod has been the 5star tuner and the spd y pipe. Oh, and the glass packs the po put on. Gotta say, I love the tuner and the y pipe. They bought me .5-1 mpg when I can keep my foot out of it and they make a big difference in the way she plays.