11 is not "normal." My 96 F350 powerstroke, with an AUTO, would get 16-18mpg.
Sounds like you guys have a bad fuel system, poor injectors, or boost leaks.
Checked mine at fill up today 12.3
Was your 96 4 wheel drive?
Was there not an HP difference from 96 to 2001?
I have know lots of ford owners that have the same mileage 11 to 14tops chipped out .
BTW If he is going by the Electronic readout on the headliner console it is never right when I check actual mileage to gallons at fill up.