im not a DP (but ill give you numbers as a reference)....i believe our 12speed tranny makes the world of difference (although our larger than most, 12.8L, engine could help).
We weight in at slightly over 32k lbs (w/out the toad), and that included 150g of fuel & 220g of fresh water.
We score a very consistent 9.9 MPG (houston to virginia & back - which we run several times a year) and thats w/ the cruise set at 72 mph (w/ the occasional right foot assistance to 80, where necessary).
Worst I've ever seen was 8.9 mpg (we were trying to make up some time).
BEST I've ever seen was 13.3 mpg (blacksburg va, to destin fl) w/ the gen running (and a few hour nap in a rest area) and towing the jeep....average speed was 60 mph (when rolling).