You had me scared for a second. . .I thought you were talking about towing at 80 MPH.Dad gets 18-20. If he keeps his speed down (70 or less) it goes up more. He gets pretty excited at 21+. He is running the tires at about 70psi.
On my '05 I pretty much guarantee myself 20mpg if I set the cruise at 70 or less (unless I have a headwind the whole trip). 75 = 18mpg, 80 ~16.5.
Towing my trailer in the above post, they did pretty similar. I didn't do back to back runs, and temperature, load, wind, direction all factor in. My worst on the '05 was 12 (headwind), but averaged 13-14, high 14.7. The 01 did the same 13-14 from what I remember, but one time I had a good tail and got a hair over 15. Towing speeds are 60-65.