Even with good gears and a light foot, don't expect to get much over 14-15 mpg in town; or 21 mpg on the highway even with mods. This is just a law physics with a 4500 lb truck with brick-aerodynamics and a 4.0 OHV engine that was designed more for torque, with fuel efficiency taking a back seat.
With all the mods I have done, I've gained about 1 mpg.
I keep meticulous mileage records.
On average, in winter the mpg decreases by a little; my limited knowledge of gasoline attributes this mpg loss to oxygenated gas and to lots of open-loop (warmup higher idle) operation.