For serious milage try look into this. Gearing, do be carefull tho to high of gearing will ruin transmissions. Tires, Lowest rolling resistance possible brand tires are needed. Areo dynamics, You might want to look into a tanoue .05% increase is allot. Tuning! PPE or EFI live software. Demetri Milard (Diesel Power Chanlange winner) used tuning to get excellent fuel econmy on a 1000+hp Duramax! Driving style! might have to change it for fuell ecconomy gains.

Two sites to look into:
You can then track your progress with this site:This if your serious in getting some decent gains in fuel ecconmy. my information might be overkill but you can get some good insite to do some of this. should be no problem getting close to 28mpg with some change in driving habits and mild tuning.

 

mine gets about 22 or so and its got 5inch lift 35's and 4inch exhaust and a edge juice

 

The easiest way to increase mpg is to change driving habits.

Let of the pedal and decrease your cruising speed.
Above 50 mph wind resistance increases per square. So if you want to gain mpg stay below.
Avoid rapid accelerating and braking. Rollout in front a traffic light and use the momentum to accelerate.

Simply drive like a grandma.

- Inflate your tires to maxium allowed pressure.
- Kick away those AT's and get pure street tires.
- Avoid to drive with open windows or A/C.
- Dissassemble unused accessories.

Decreasing weight in a truck?
Wold work in a passenger car but a truck is already to heavy and has a shape like a brick.

Height:
According to the Bosch automotive technical handbook a decrease of riding height of 1" lowers wind resistance by 2% - neglectable...
(wind resistance is not fuel consumption in this case!)

internal engine resistance:
friction is a major problem. use of synthetics lowers friction by 2%- neglectable if you go for decreased fuel consumption, because syns are way more expensive and will eat up the fuel savings.