He or She may want to put a few more miles on it as the engine is barely broken in.
I was highly disappointed in the mileage I was getting and considered trading it in until it turned over 35,000 mi (~ 65,000k). From that point on, I have been getting ~ 15 - 16 mpg city & 18 - 24 mpg highway on 87 octane pump gas. And yes, it DOES matter how hard you have your foot into the accelerator so don't discount that advice. I do have the 3.71 gears and 4x4 with full up skid plates and heavy ga steel bumpers so it is at the heavier side of the weight scale.
I too am guilty of occasionally leaving it in 4x4 for more miles than it should have been (but not a week at a time) and the mileage dropped by about 3 mpg City & Highway and shows up rather quickly on the fuel gauge.
Watch the air filter and don't just knock the dust out or vacuum it off occasionally. Change it. 3,000mi for oil changes. Proper oil weight (for your climate), clean oil does make a difference for mileage.
Then there is a possibility that that particular 3.7 is a lemon.
Hope this helps...J