OK, I'll play this game...
We have been on the road for the last 10 days in northern NM and Colorado. Our 2012 Nexus 24' C has (over the last two years and 25,000 miles), always averaged 9.5 which includes a little generator time. Since fueling in Santa Fe and heading up into the southern Rockies (Taos, Angel Fire, Durango, Silverton, Ouray (yep up and over Red Mtn pass at 11,000+' on the "Million Dollar Highway" - Awesome, white knuckle road), Aspen and up and over Independance pass at 12,095' at the continental divide, and Monarch Pass at 11,300' along with about a dozen lesser passes over 10,000' we are averaging a solid 9 mpg.
I can not say enough good things about the smooth power of our 6.8L V-10 mated to the 5 speed Torque Shift trans and 4:10 rear end. We are running at our GVWR of 11,500# but several thousand under our GCWR (I am towing my BMW R80 RT - bike and trailer weigh 850#). Have gotten up and over every pass either at the posted speed limit or easily keeping up with the flow of traffic (not always the same thing).
While you lose 3% of your hp for every 1,000' of elevation with a naturally aspirated gasser there is a commensurate drop in air density, reducing drag, which appears to pretty close to cancel each other out.
Just some real numbers from the road.
:C