The trans is a 4R75.
The worst mileage I've ever counted with my F150 was just over 10mpg on my last tank, 90% in town, very short trips, lots of idling, winter gas, etc.
Typically I average 12-14mpg with mine. This is with 35x12.50s, 4.56 gears, 93 octane performance tune. With 3.73 gears the...