6.0 has a series of common problems that once addressed, the engine settles in and becomes really reliable. The known weak points and problems:
head bolts, and by proxy, head gaskets
oil cooler
EGR cooler
up pipe bellows
fuel pressure
FICM
water pump.
ARP studs and Fel-Pro gaskets, along with 6.4 pushrods and a careful check and machining of the heads and checking the deck for flat fixes the head problems.
A new factory oil cooler and a switch to a true diesel coolant, or the Bulletproof Diesel remote cooler and filter fixes the oil cooler.
Bulletproof Diesel makes a one and done replacement for the EGR cooler, or delete the dang thing and be done with it.
Rudy's diesel has the up pipe with a flex joint.
Blue spring fix from Ford for fuel pressure.
Several aftermarket sources for FICM's with higher quality parts, and steady voltages. The Atlas flash restores the power Ford took away with their updates.
There are water pumps out there for both early and late builds that have metal impellers.
My old 6.0 was a pleasure to drive, and was totally reliable after mods.
6.4's with the twin turbos have their own set of issues, including valve tip and rocker wear.
First edition 6.7 had ceramic turbo bearings that some folks have had problems with. I stress "some" because there are lots of high mile early builds that keep on rolling. Later models, the turbo was changed, and programming changed with it, increasing HP and torque.
The latest 6.7 is just the cat's behind, the shiznit, the wow that Ford drivers have wanted since the 7.3 went away. The turbo is in the valley, with short runners to inverted heads. Turbo lag? What turbo lag? Power? Anyone says you don't need 890 foot pounds of torque, just don't talk them any more. You don't need that kind of negativity in your life.
My 2016 does everything better than my 03 did, PERIOD.