The later model trucks used a variable valve timing setup that boosted both low rpm and high rpm power by advancing the cam at low speeds and retarding it at higher speeds. This does help with economy as well. MDS was first implemented in 2006 if I recall. Both of those together probably add up to at least 3-4 mpg at freeway speeds. Since your truck has neither, you drive short trips, up hills, etc....your conditions are not optimal but 7 mpg is not good.
The 4wd does not help the numbers.
My 314,000 mile 2007 Ram still gets 16-17 at freeway commuting speeds. I have never checked mileage for any other condition.