With my 3spd, 1st is plenty deep enough to get me going with 3.25 gears. AND i got 14.5 MPG on a recent trip to auburn. If I had taken the highway (as opposed to the interstate where speeds are ~80), I am sure that 17 MPG may not have been out of reach. Keep inmind that I have a gas hog 500 cfm holley too,

 

How about just putting larger tires on? It's a 4x4 right? Larger tires will lower your effective gear ratio.

BTW, if you are looking for good miliage in a fullsize pickup, you are looking in the wrong place.

I would look for a 4cyl 5 speed Ranger 2wd. Or a small V6 4x4.

 

I have seen a couple sets of 8x19.5s on highboys and always wanted a set. I think they would be about 35s. Wide tires cut down your mileage too. Tall and skinney is best for fuel economy.