HOW you drive is key.
flat roads and 50 to 55 I average 17 to 19...
freeways at 65 I average 16.
town is 12.
mine is 2 wheel drive. 6.2. 3:73. and go easy starting from a Stop.
towing 9,000 pound trailer .. 9 mpg.. over 1,000 miles.. and lots of hills.
if gas mileage is that important... second CAR.. or keep the OLD truck.
FYI. a V8 car from the 1960's got 12 to 14... on the highway. and half the weight and size of a F 250.
so the modern F 250 does very well at gas mileage for what it is. a Hard working WORK truck
my opinion.