I drove from Wichita to KC last week, 65mph and got 21.3 mpg. I was in a hurry to get back and drove 75 all the way, and got 18mpg. Both unloaded trips and hand calculated. Wind was calm. Speed definitely makes a difference.
I pulled a small flatbed trailer same trip on other time to KC, weighing about 2000 pounds. At 65 I got a hair over 18 on that trip too.
I like my truck!