I'm going to read all (5) pages of the replies, but just wanted to join the bad lifter party. Trail Boss LT 2,990 miles. Built in January 2021. The bad / stuck lifter caused the push rod to bend. Lots of misfires..etc Horrible situation, as it occurred on vacation about 150 miles from home.
I just got my truck back 5min ago, I was comparing the repair order notes to what I'm seeing online. Took 3 weeks to get the truck back because of backorders on all parts involved.
The service center mentioned this is a problem with the 21s, but mentioned that the new OEM lifters from GM are "updated" parts compared to what was factory installed just a few months ago. My biggest complaint here is that (1) it wont be a recall because too much labor is involved, (2) they didn't replace all of the lifters while they were in there, that's not how GM operates.
I have read other forums that blame DFM as well. Perhaps I will buy the (~$200?) kit to prevent this from happening again