I have a 2009 2500 Suburban. It gets around 14 mpg running "empty" which is just a driver and some tools in the back. When I pull my boat I have my family of 5 in side and the boat and trailer weigh about 6,500 pounds total. I get about 10 MPG with the boat. This is generally all highway and interstate driving. I use cruise control the vast majority of the time and set it to the speed limit when not towing. When I am towing I set it to 65 even though the speed limit is 70.
My Suburban has 3.73 gears in it. I really wish it had 4:10. Not that it tows bad now but in rolling terrain like we have in VA and WV it seems like I'm always either downshifting to go up a hill or downshifting going down a hill to keep it at the cruise control speed. I've found that if i lock out 6th gear it maintains speed both up and down hills a lot better.
