there were the 6 part videos by the powerstrokehelp guy, you'll spend 40+ minutes watching them all plus other relevant ones. going from memory i want to say if you were serious about spending money on a Ford diesel truck the best to chose is a 6.0L and put $5 grand into the motor. I think the big thing was head studs, the 6.0L will get the best gas mileage and run the hardest. the later year 6.4L and 6.7L are plagued by various emission devices and DPF that you can't necessarily remove. And i want to say the 6.7L was shown to have bad cylinder head valve train design, they are only going to last 100k miles before the valve train needs to be rebuilt. again, i'm going from memory. if you are looking to buy a ford diesel truck you should watch the videos so you know what to expect.
http://www.youtube.com/user/powerstrokehelp/videos
---> http://www.youtube.com/watch?v=HL_5ACtAjLs&list=UUQz2vFEc1m-WGKf6g-pz9DA
http://www.youtube.com/user/powerstrokehelp/videos
---> http://www.youtube.com/watch?v=HL_5ACtAjLs&list=UUQz2vFEc1m-WGKf6g-pz9DA