I think 300000 miles is on the low side. I know this is the same as the 5.9 with 2 fewer cylinders. They will easily run 10000 hours if maintained. I have heard of one with 21000 hours without being overhauled. I don't think the parts are too expensive either, I would think you could buy an overhaul kit for 7-800 dollars but of course a valve job would be on top of that. You would also want to go through the injectors, not terribly expensive but definitely another expense. They are a great little engine.
