Sounds all normal.
With my 5100 Lbs. V6.
In the winter time I get 14.5mpg...crap gas and I use the 4wd more.
In the summer I can get up to 16.1mpg.
To make sure your getting your best mpg...
Tire pressure.
Change the front and rear diffs and the center gear oil.
Clean air filter and clean motor oil.