I just did a cross-country trip in August/September:
Way out: Denver to Portland, Maine (approx 2,000 miles) and got 16.8mpg. many sustained periods of 85mph +, and also garbage gas in Nebraska/Iowa with far too much ethanol that knocked the trip mpg down to low 15's. Once we could get 91/93 again we jumped back up. Not bad for blasting the throttle many times to pass trucks and such on I-80, and my gf is starting to get a heavier and heavier foot each time she drives the truck lol
Way back: LBI, NJ to Denver (approx 1800 miles) ended up at 16.3 mpg. Prior to our last day of traveling, we were at 17.4mpg. We had to fill up in Nebraska with 87, so things fell off of a cliff. We also were driving ridiculously fast and had a great road partner in a current gen Cayenne driving between 95-100 for a few hours. I also made the mistake of throwing it into sport mode as I was dying to get home, whoops.
My lifetime mpg is at 16.3mpg now at around 11,000 miles on the odometer. It was at 16.8mpg until that last day in Nebraska, sad.
I will say, the truck is probably the best road trip vehicle I have ever been in, topping my previous favorite vehicle (E39 M5). Extremely comfortable, decent mpg for being what it is, and effortless passing with a blip of the throttle (especially if you are in boost already). Very impressed and love the truck even more. Now, to get back to some trails and go find some desert before the snow comes here in Colorado.