Known issue. Still under 5/60,000 powertrain warranty. All new lifters in both banks, new push rod and camshaft, guides and seals.
$0 out of pocket.

I had a look at the warranty claim from the dealer to GMC, was just under $10k.

I just noticed it running rough suddenly with a little bit of a vibration. No check engine light or other dash indication. I took it to my local mechanic and his fancy OBD showed no engine codes, but further digging showed dozens of misfires on a few cylinders over time. Considering the major damage going on in there, I certainly would have expected it to throw a code. He initially thought bad fuel or too low of an octane.

If you have a late model GM 5.3, be vigilant. Once your 5/60k is over, it's on you.

(I knew about this issue before I bought it, but I asked the service manager directly if this was something to be concerned about. He said that they checked all 5.3's on their lot and put them through diagnostics while running to make sure none of theirs had the issue..... he acknowledged there was a concern, but all of that dealerships vehicles didn't have the bad parts and it was easy to tell by taking the steps he did. Complete and utter falsehood)