Owned an 04 6.0 and drove an 05 for a couple years. I never had any trouble with either, but quite a few folks did.
Biggest problem with the engine is the E.G.R. valve gets dirty and sticks, causing all kinds of other problems. The engine is out of warranty by no, so there is a very simple E.G.R. delete that solves that problem.
Some other folks, mostly with chipped engines, had head bolt/head gasket problems. Pretty unusual on a stock engine.
And for a pretty good percentage of folks you'll get advice from, the Cummins is the be-all end-all of diesel pickups and anything else is trash.
Cummins technology is falling behind the last few years (too many compromises to meet new emissions standards), and it's biggest issue is the truck wrapped around it.
All three make good trucks, it's personal preference.
