Unfortunately, the combination of a heavy truck, 4wd, the 6.0L motor and
4.10 gears will conspire to keep your mileage in the low teens at best.
Everything about this combination says "work" or "hauling" or "towing", and
nothing about it says "economy". My truck isn't set up like yours, but I
have friends with similar and when we get together to swap lies they say
"around 14" for mileage, which I guess isn't too bad. Depending on your
type of commute and the weight of your right foot, I think you can expect
around 12-14 empty, and maybe 8-10 with your trailer.
Don't bother with a high-flow air filter - save your money. A chip and
larger exhaust might help a few MPG but they are mostly geared toward adding
power than mileage. The only thing I can really think of that may help the
most would be to drop down to a 3.73 rear end, but since yours is 4wd that
may not be the best, plus you may (I don't really know) have to change out
your front gears also and that's going to get into some serious $$$.
Good regular maintenance and a light foot will help you stretch out your
mileage more than anything else for the money.
Cheers - Jonathan
Jonathan A. Race
Lieutenant, EMS Supervisor
Click to see the full signature.