Last week, I took my 2014 Denali to Austin to see my sister for Thanksgiving. I left on Wednesday, and took I-35 from Ft. Worth to Austin. After some traffic bottlenecking and some 55-75mph driving, and some length stops idling, I achieved 22.4 mpg. The truck was 2/3rd's 87 and 1/4 93 octane. Trip started with 86 Miles on the truck.
On the return trip, toping off with 93 octane and no stops, alternating between 68-75 miles per hour, the result was 22.6mpg.
I am very impressed. No tail wind on either trip. My 2011 Denali would get 17.5 at best. Gotta love AFM!
Will