3 of them have the 3.5, and one bought an '18 F-150 Platinum diesel a couple weeks ago. She says the diesel is getting around 20mpg everywhere, and mid 20's highway.
So very similiar to 3.5 mpg.
As for 15-16 mpg with a lift and big tires...that is Really Good. The lift hurts the mpg more than the weight of the bigger tires too. I had an 01 4Runner years ago that I put 1" spacers on the front, and +2" springs in the rear, so it sat level. Mpg instantly dropped from 17 to 14, and I have experienced this in many vehicles, a few of mine and many of my friends trucks.
So getting 19 to 23-24+ mpg with a full size truck is really impressive, especially with so much power, even more than the 5.0, actually 100 lb' of torque more, and without the racket. I love the sound of a V8, and I'm a Ford man, but like a quiet vehicle as a daily driver. As expected, the V6 makes no noise at all, where as the 5.0 growls everywhere it goes, and it sounds great, just gets old fast to me if it's not a hotrod