on road trips i have seen as high as 14.5 mpg thats just loaded with crap for camping..ect nothing crazy.

what i have found over the last 3 years and 45k miles with all of my V10 4x4 3:73 excursions.

summer time
8-10 mpg city 12-14.5 mpg highway

winter time(running 4x4 all the time and idle time)
6-8 mpg city 10-12.5 mpg highway