My info is obtained from first hand experience from friend/family/company trucks (not that that has a lot of weight...). Tests on the net seem to back it up as well. Here is a test from Edmunds on a 5.0 F150. They netted close to 20MPG.
https://www.edmunds.com/ford/f-150/...my-test-27-liter-ecoboost-vs-50-liter-v8.html
Edmunds also says that they got 16.6 MPG with the Tundra. (4.3 gearing probably hurts them here).
https://www.edmunds.com/car-reviews/top-10/fuel-economy-for-2015-full-size-4wd-trucks.html
I don't know how credible those results are, but it seems like they've at least eliminated most variables by conducting that test in a more or less controlled environment.
_
Again, I drove my father's 4WD Tahoe (5.3L V8)--600 mile trip, 4 adults, 2 kids loaded with cargo, going 65-75MPH (avg of 70mph most of the way), and we were at 22mpg. I haven't seen a single test for the Tundra getting anything close to that. Have you? Three Tundra 5.7's I've been around for a while have never broken 17mpg, and typically average 15-16mpg (hwy). A friend also has a GX460 getting 12-13mpg avg, and 16mpg highway (I know, different engine and FT 4WD, but thought I'd throw it in). Again, small sample size, but that's what I've seen.
_
BTW: The link you posted--You've got a HD Payload pkg picked out for the F150. Regular F150 (comparable to the Tundra) comes in at 15/21.
https://www.fueleconomy.gov/feg/Find.do?action=sbs&id=36810&id=36546&id=37052&id=37050