I can't help you with the 5.4 engine.I can say that my reg.cab,V-10,man.trans.,3.73 axle just averaged 13.86 mpg on the last tankful of gas.It has 3000mi.and this average was mixed driving and not being very conservative with the gas pedal.The first tankful when new was 11mpg.and this was driving pretty conservatively.
oh oh oh, i can, i can!!!!! i have a 5.4, 6 sp, 4:10 gears, extra cab,& long bed. the best mileage i have ever got was 13.5 mpg. the worst was like the second or third tank. i got like 11 mpg. it has got better since i bought her new though.
The last two weekends driving from St.Louis to Lake of the Ozarks I have been getting a little over 15 mpg. I have a 2001,f-250,5.4,3.73,sc,lb. This is the best I have ever got. I usally average around 13.5 - 14.5 around town.
I've got a 2001 F250 4x4, 5spd, 5.4, reg cab, long bed, 3.73, 265 A/T. I've installed a Gibson cat back, K&N FIPK, and Superchip. Any mileage savings expected by these mods is null and void because of my biggest power adder.....a size 13 lead foot.
On average, I get 13 - 14 mpg. That is with a work cap, passenger, and 500 - 1000lbs of equipment. Also, I drive mostly in a mountainous area. I've had a best of 16 - 17 and a worst of 11- 12.
Sometimes I'd like to have the V10 just for fun. But the 5.4 is a great engine and I love it. It suits the demands I have for this work truck and then some. Good luck.