Question about fuel mileage on F150 suddenly cratering

Started a thread on the OB as well but prolly should post here for the higher traffic

So I own a 2017 F150 with a 3.5L ecoboost engine in it with 9,830 miles on it and am on a trip Pheasant hunting in South Dakota


We left from Memphis which is roughly a 1,000 mile drive one way. On the way up here we ran 5 over the speed limit and according to the truck averaged about 20 mpg all the way to about Mitchell, SD and got gas then noticed the MPG just start falling severely.

We drove prolly about 100 miles while at our hunting location with the mileage remaining pretty poor. We are now on our way back to Memphis and reset truck mpg, running the same speed as before, having bought a new tank of gas in Mitchell. We have made it to Sioux Falls since the reset (about 140 miles) and the thing is averaging around 11.5 mpg still

Wth is going on with this? Bad batch of gas or something??

Obviously it's much, much colder up here and the elevation is different but there's no way those things make this big a difference

I'm pretty confused bordering on concerned at this point as our mileage on a 1,000 mile trip has been essentially cut in half