Jmoore- Have you done all the usual maintaince, like the little stuff? Good air filter (or DIY cai), new plugs (stocker coppers), cleaned the tb, etc? These guys are getting pretty decent mileage out of their rigs with not much more than proper maintaince and FULL synthetic fluids. I haven't been able to foot that coin yet on either truck, much less both, but from what Ive read, guys are picking up a mpg, maybe two, just from running synthetics in the motor, tranny, diffs, and transfercases. A $100 (tops) e-fan also adds another 1-2mpgs, plus a little power.
I need to take my own advice, especially with the Durango, but the time will come for both trucks to get the treatment they deserve....
--- Also, the only reason I stated all of this was because you've only had the truck for 3 weeks, not assuming you don't know whats going on, just throwing it out there.
--- Also, haha, are you getting your numbers from your overhead, or from calculating by hand? Dont ever go by the overhead, fyi