1996 F-250, 7.3 single cab, dual tanks.
  I'm going off of someone elses word here and I find it hard to believe.... two tanks (you know the capacity better than I do) He claims no better than 10 MPG, and I said no way. The truck has 145,000 miles on it, low geared (granted) and has a heavy shell on the bed, but 10mpg????????
  No load, no trailer, no weight, and 10 MPG? Highway driving?????

1996, reg cab, long bed.

 The thing (when I drove it) felt like the 'ole diesel wanted to part ways with the mounts when pushed above 2500 rpm's or so... and I blamed it on gearing and solid axles.
   
 10 MPG? eaven not runing right?
What should a 1996 Powerstroke (ummodified) get mileage wise?

 It showed signs (recently) of mechanical pump failure, (no power suddenly and then resume normal).

 I think I'm answering my own question, but just for other viewers sake... Can a worn out mechanical pump "float" and cause a loss of power? Would that effect fuel mileage?

  I replaced the pump earlier today (pull the filter housing with the pump... no need to remove the turbo) and the thing pulls (seat of the pants observation) better than before, with less shudder.

 Still, I have to question the whole 10mpg thing  

10 mpg unloaded is pretty bad. I'd say there's a problem with it somewhere. Short gearing can really eat up fuel, but sounds like it needs a tune-up, and possibly some fuel system work.  

i have a 95 and a 97 with 4.10s and they get 10 no better no worse  

dad has a 94 turbo diesel and it gets 10 no better no worse...  he also has a 08 f450 it gets 10 no better no worse...  i have a 08 powerstroke and it gets 13 no better no worse. mom has a 2004 powerstroke... it gets 19-20   so i dont really no what to tell you...   your 97 should get better then 10 i would think  

my 97 gets 18-20 when i drive like i OWN it but when i drive it like i stole it then its gets 16-18 but its fun blowing smoke at the ricers and hybrid owners  

I'm getting 15.5 mpg out of my 1999 7.3 psd, but I DRIVE LIKE I STOLE IT and I ALWAYS HAVE THE A/C ON !!!  

I've got a 94 w/ mechanical injector pump and im getting 11 running around town.  Getting 16 on the interstate.  

Ihad a '97 7.3 4X2 Crew Cab w 5-speed & 4.10.  Gave it to my son for his business.  247,000 and gets 17 around town carrying over 1,000 lbs. A fuel leak is the most likely culprit. Had to replace the fuel filter bowl and fuel pump at 220,000 miles. Fuel leaks into the valley below the filter then down the back of the engine.  Check your parking spots for stains. Got about 8 to 10 mpg during the leak. Haaven't added any modifications.  Still bone stock and doing the job.