Power steering hydroboost started leaking around 30k, and was replaced under warranty.
Transmission was replaced at 50k because of a weird shift flaring issue that was intermittent. The trans worked fine and was tight, but I complained enough of the shift flare that they replaced it with a re-manufactured unit.
The EGR cooler failed at 84k miles. The oil cooler and EGR coolers were both replaced at this time. This is a very common issue on the 6.0 diesels.
At the same visit as the EGR cooler failure, I advised them of a small oil leak since my warranty is running out in a couple of months. They diagnosed it as a rear cover seal. The resealed the rear engine cover and replaced the rear main seal as a preventative measure.
I absolutely LOVE LOVE LOVE my truck. I wouldn't want any other engine in my truck besides the 6.0. It's awesome. It is the last real diesel in my opinion. It sounds like a traditional diesel. The newer trucks are all quiet and have even more emissions related crap than the 6.0.
Most of the problems with the 6.0 engine are related to government mandated emissions equipment. There are many common problems with the 6.0, but if it is kept stock without tuning, it is very reliable. The rest of the truck is BUILT FORD TOUGH like always. The interior is amazing, especially the King Ranch. The transmission is awesome. The Dana 60 front axle is super strong, unlike that independent front suspension crap GM is using now.
If you tow a lot of weight all of the time, you could maybe expect some head gasket issues. To keep that from happening you should: Replace head gaskets, mill heads to make sure they're flat, and install ARP head studs in place of the head bolts Ford uses.
An aftermarket coolant filter is also a must to remove the remaining casting sand and particulate in the coolant that will eventually plug the oil cooler, and cause the oil cooler and egr cooler to fail. This is the primary reason why they fail.
Change the oil every 5k and fuel filters ever 15k and you'll have a super reliable truck. I also run 1 oz of 2-cycle outboard oil per 1 gallon of fuel to keep the fuel injector and upper cylinders lubricated with the new ultra-low sulfur diesel fuel.