I've got a feeling that he didn't refill the DEF(diesel exhaust fluid). A guy around here I talked to said that he didn't refill it once and it dropped to about 10mpg. He's got about 15k on his regular cab and says hes running 17 for all around driving

 

WOW Thats a 40% decrease in fuel milage. It sounds like there is something wrong with that engine or transmission or both. I dont think I would guage a vehicle's performance and durability by one that is only 60% fuel effecient as it was.
I have a 1995 F250 and it is a gasoline engine with 260,000 + miles. I just replaced the transmission a couple of months ago (the origional was still in it), the U Joints, and the oil pump. I immediately got a 35% increase, 10mpg to 13.5mpg, in fuel milage, and did no major work on the engine. I know there are differences in diesel and gas engines but I drive mine across country and pull trailers occasionaly so I would think a diesel would fair better than my old gas engine.
Anyway, hope you find the truck you want

 

Do not get the gas for a truck you want a plow on. The reason you can not find many diesels at great prices is because of how great they are. My 2008 250 4x is gas, I love it. I also knew that this truck would only be hauling heavy loads every once and awhile. Average mpg is 13 at 70 mph, 11 around town with out trailer, but with about 1200 lbs in bed. Was worse than this till two weeks ago, found out I had a rear caliper sticking. Truck never pulled to one side though. Rotor, pads ect all toast.

Think about the maintenance to be done after your warranty expires. What can you do your self and what do you need to shop out? Some repairs on the powerstrokes require the whole cab to be removed. A daunting task for any back yard.

As far as the $ 50 k. Worth every penny. When you buy new, you know how your vehicle was handled during the early parts of its life. Treat them right and you will get the same in return.

Bully Dog can get you the black smoke you hunt. LOADS OF POWER.

 

Ok my truck is a 6.2 four door FX 4 with 3.73 gears I get 14.2-15.8 around town I have gotten 18mpg on hwy. I have a 96 F350 7.3 so I have a diesel and Its like new and runs even better so I didnt spend the extra 7 grand. truck was already 50k. I love the gas motor for everyday stuff, if I had to tow alot go diesel.