I am getting 16 hyw at 78mph and 13-14 city.
Just towed a 23 ft V nose trailer with only 1 snowmobile in it 250 miles and had to get fuel. burned 29 gallons! thats less than 9 mpg.
Same trailer with 3 sleds in it with my 2008 Cummins got 16-17. That was with all deletes done.