I have an 06 LBZ and one thing has gone wrong with the engine. #8 glow plug went out around 65K. I think it was $28 bucks or so but it was under warrantee so I let them do it. That's it.
The other things I have done to the truck:
Steering clunk. (Look it up)
Steering column bearing at around 50K. What the ??? Truck has never seen a dirt road! :M
PS hose leak.
Engine oil cooler hose leak.
Oh, and it needs new shocks. (hell, it needed those at 20K!!!):M
That's it.
As far the 6.0 goes, I'm not a fan of them. BUT, if gotten cheap enough you can Band-Aid them up and they make a pretty nice engine. The rest of the truck is light years ahead of the 7.3 PS.
It just depends on what you want and how much money you have. Good luck hunting.