After almost 30,000 miles, this is what I have found
Unloaded
65 mph about 14.7 to 15 with 4.30 final drive, 2000 rpms at 65 mph
75 mph about 13.2 mpg
Towing
63-65 mph at 17,000 lbs with a tall (13'5")toy hauler is 9.2 mpg
70 mph at 17,000 lbs with a tall toy hauler is about 8.4 mpg
75 mph at 17,000 lbs with a tall toy hauler is about 7.3 mpg
Towing with a goose neck triple axle only 9' tall at 13,000 lbs
70 mph about 11 mpg
Over all very easy to drive no matter what you are towing. The truck will go as fast as your pocket wants to afford. Cruise control works very well with either trailer.
Mark