There is one item to consider about a 7.3 diesel in a Ford. Ford's powertrain warranty covers the engine until 5 years or 100,000 miles, whichever comes first. There is a 100.00 deductible for each visit. In a perfect world, you could look for a F250 or F350 just less than 5 years old, and with less than 100,000. Check it out for any major engine problems and get them fixed before the warranty expires. At a recent national Ford meeting, the head of the Ford Parts and Service division state that the super duty truck owners were Fords most important customers. They know that the 6.0 has had some problems, and are willing to provide some assistance even in "gray area" warranty concerns. The original owner does have a little more leverage than the second owner however. One thing to look for when looking a a diesel is the air cleaner. Nothing will kill an engine quicker than a poorly maintained air filter. Dirt ingestion will kill a turbo and piston rings quickly. Beware of K&N type aftermarket filters. K&N says there filters never have to be replaced. They do need to be cleaned. I have seen several used diesels come into the shop with a K&N so stopped up that they have been sucked flat trying to get air past the dirt on the suface of the filter. Some people think that if you never have to replace the filter, you can just put it in and forget it. That is not the case. When looking a a used truck, a clean air filter may be a sign that the owner has taken good care of it.
