Professional
It depends:
12 mpg = 80 mph into 50 mph headwind
23 mpg = 80 mph with 50 mph tailwind
About 17-18 mpg almost-all-highway average for me. '05 4.7L CC 4x4.
12 mpg = 80 mph into 50 mph headwind

23 mpg = 80 mph with 50 mph tailwind

About 17-18 mpg almost-all-highway average for me. '05 4.7L CC 4x4.
Veteran
Well, with 1/2 the tank I have just run with "mostly" highway driving, I got about 17.
i have a '05 dak w/v-8, and the getrag 6 speed. If I accelerate gradually, and drive conservatively (not that it's any fun) i can get around 20 mpg based on the on-board computer, currently i am at 20.3. And that is around town driving. I can go a month on one tank and since it costs 60 dollars a tank to fill up, i will trade the acceleration and torque, unless I really need it. Besides, the tranny has really broken in well, shifts crisply.
Rookie
road trip - 18 mpg average. just driving around town, usually 15mpg.
my 3.9L mods are superchips tune, v8 throttlebody, 180* thermostat. truck weighs 4240 pounds.
my 3.9L mods are superchips tune, v8 throttlebody, 180* thermostat. truck weighs 4240 pounds.