Finally had a chance at a good long run... a round -trip from Mesa, AZ to Vegas. That's 684.4 miles. Total MPG was 25.7. That included some small portion of city driving. There was one leg that was pure highway in light traffic of 216 miles. MPG for that segment was 26.2. Just turned over 3K on the odo during that trip so I hope mileage will continue to improve.
I've hit very nearly 29mpg when I'm driving like a grandma on gentle hills. OFF the cruise control, so I can coast down and use momentum to get me partway up the next one. With the hilly, twisty highways in my area, speed limits are mostly lower, which helps a lot. Some stretches top out at 50mph (and 35 for trucks).
My current mixed tank is averaging just a touch over 24mpg, and that's mostly suburban driving (plenty of stop and go, but not quite as much as downtown, and lots of cruising at around 40 give or take).
I also do a fair bit of driving on gravel forest roads where I often use 4 hi because it makes a difference in stability over the washboarded crap.
In wintertime, I topped out at maybe 21 or 22 if I really pushed it on highways, but most tanks were around 19mpg. Winter gas, colder temps, etc really seem to affect this truck.
overall, I meet or exceed the ratings considering that wintertime is less and summertime is better. Mine is a 4x4, as well.