[rare86]

Ive got an 08 excab 4x4, 5.3, 4sp w 3;73 gears. Im a little over 118k mile on it. Ive run Amsoil synthetic in it since about 25000 miles. Have been running 10 ply 285/65-18s on it since around 48000 Put flowmasters on it at 78000. (love the sound.) on highway running 70mph I have seen a little over 18mpg. at 80 its down to about 16.9. My truck has a shell on it and i carry about 400-500 pounds of tools and equipment in it all the time. I do alot of off highway driving and it averages 14-16 mpg per tank depending how much off road is done.
I had an 04 4wd excab Silverado set up very similar to this truck doing the exact same job. I actually got a little better mileage out of the 04 on the highway (19.5 on a few tanks) but overall it wasnt alot different from the 08.
Basically, the afm hasnt shown me that its worth even mentioning on paper. I love my truck, but that is definately not a selling point for me.