The old 6.0 with 4 speed and 4.10 will easily get 14 on the highway so I would think the new 6 speed and 3.73 would do somewhat better. I know my truck runs 2500 rpm at 70 mph and still gets over 14 strictly highway. That is with the 4:10 rearend. Drop back to 65 and 15mpg is attainable.