The motors are good motors, but they knock on startup when cold. Its not a bottom-end knock, more of a tick. Something to do with carbon in the top ring groove. Goes away at operating temperature. Seen/heard them doing it with as few as 9,000 miles on them and have driven one with 120,000 on it that still ran great and used no oil (but knocked on cold startup).
GM knows about it. Has dealer bulletins on it. Refuses to do anything about it because they swear it is not a reliability or longevity issue and it goes away when warm...
Other than that point, I know of no other issues at all and I've been involved with a good number of them.
Own one also ('00 YukXL that wife drives).