I had a 93 F-350 with the 460 engine. Id say that motor
got about 8-10 mpg, so id say the 351 engine would be around 12mpg. One word of caution on this vehicle, check the oil pan for rot. Youd think the dealers would carry oil pans in stock WRONG!...its was a nightmare trying to get one. My truck sat for two weeks waiting for this part. I think the truck is awesome to work with, and a beast for plowing, infact i bought another one 95F-350, and made sure i undercoated everything vital underneath. Good luck!
all ford oil pans have a rotting problem,it seems like the 351 is the worst,The 351 will be lucky to get 11 mpg-my old boss ahs one,its a pig,but its a HD truck and can handle a plow great with that nice Dana 60 front end.the F350 is sprung very stiff,even with 1000 lbs of tools his still rides real hard,tough on your back.