Here is my experience.
Driving to work 110 miles per day empty:
City and highway hammer down. 16.7-17.5 mpg.
City and highway driving keeping tach under 2k and driving 65 mpg or less. 19.8-21.3 mpg.
No mods other than not wearing my lead right shoe.
Driving with the camper onboard and a 16' trailer and my Zuk on board the trailer.
Last trip to Ohio I got anywhere between 12.8-13.7 mpg loaded heavy and towing thru the Blue Ridge Mountains. I left the lead shoe home on this trip. I was happy with that result.
My trucks mods:
SCMT @ 90 hp
4" DPPI Exhaust
Motorcraft Donaldson Intake and Filter.
Here is my newest mod. It gets 32 mpg. It beats a tank and a half of fuel per week. Fuel here is $3.299 per gallon.