2008 Tundra CrewMax Limited, with 5.7L -- Just got back from a 1,750 mile roadtrip without our Bambi. 17.8 mpg mostly on Interstates at 70-75 mph, with a little city driving; Phoenix to LA (Disneyland), then to San Francisco and back. OMG, can't believe downtown LA traffic. Where are all of those people going, 24/7?
Last year, we got 23.5 mpg on a weekend trip from Phoenix to Tucson, roundtrip, without our Bambi. Drove at 65 mph on cruise all the way to save fuel (no passing). Very flat. Same trip with 19-foot Bambi is about 16.5 mpg (at 60 mph).
Earlier this summer, we towed our Bambi from Phoenix to Denver, roundtrip. All Interstate driving at 70 mph; 13.5 mpg. Usually, we don't drive this fast when towing; but we were headed to a funeral and needed to get there fast. Also, we recently switched to 225/75x16 Michelin XPS Ribs on new 16-inch wheels. I would not have driven this fast on our old Marathons or Maxxis tires due to fear of blowouts, but we no longer worry about tire failures.