Boy, seeing these numers posted makes me feel pretty good about mine. When I tow my boat 1650lb it is behind my 23 ft 5th wheel 6100lb , with an 02 GMC 2500 4x4 6 liter and I am getting 11 mpg at 100k and hour.
Glen
14-15mpg in a 1999 Infiniti QX4 with a load of about 2500-3000lbs. I am "that slow guy" and usually only do 60-65mph on the highway.