I was just visiting with friends of ours that have an 05, 4x4, 6.0. They have had just a awful time with it. 2-turbos, 3-egr valves, injectors, I forget the rest. They got Ford involved and it was still a nightmare. Ford wouldn't get involved until the started to take action on getting it "lemon lawed". Then I know a guy that bought an 06 4x4 6.0 I believe he bought it used with like under 10,000 miles. He hasn't had any trouble with it. Our friends said they know several owners of 05-06 that have had the same awful luck that they have.
Thinn=k about it Ford has changed diesel engines twice in just a few years. The 6.0 making a 2 or 3 year run. If the 6.0 was any goood why would Ford only run it a few years. It costs alot of money to change designs. Dodge & GM are still running the same diesel that they came out with in last what 8-10 years. Oh they have made upgrades but it the same engine. Now Dodge Cummins has a 6.7 diesel out. I know nothing about it. But I see the old 5.9 Cummins is still available in 08.