My dad used to have a 2000 f-350 cc
single rear wheel, 4x4
auto, he got around 15-16 or so.
My sig has mine with my mods.
Alot of it depends on how you drive, and what kind of driving you do more, like city or highway, or slow back country roads.
For instance, I know I can get 18 mpg
even with a lift and tires, but I know for a fact I CAN also get below 10 mpg
like I said, alot depends on your driving habits.
Also depends on things like proper tire pressure, lift and tires, mods, and gear ratio.
I agree with the 14-18 as nasty96 said for a ballpark.
be sure and post pics if you do get it.