It will fail at some point. We all knew that with the LS motors, and alot of us did preventive maintenance when the miles got up there or one failed. But there were only 4 in there and failure rate was lower. Seems with 16 of them the rate is just higher. Problem is it wasnt a problem to have a tuner delete the system and just use standard lifters as a replacement. After that you qwere bulletproof. I dont know anyone tuning the new trucks who could do a delete??
Just a slight correction for clarity: There were 8 collapsible lifters in the AFM engines since 2007 on the 5.3, and since 2009 on the 6.2, and the mode switching was relatively infrequent compared to the current DFM motors, which have 16 of them and is more frequently shutting down individual cylinders.
And you're 100% correct that prior to this generation of engine, it was possible to swap in conventional lifters and tune the DFM out. But now GM has encrypted the ECM so strongly that no one has broken it yet without GM's permission (e.g. Hennessy), so owners are effectively stuck with a ticking time bomb, literally, with no way to defuse it.
Collapsible lifter failures could happen in the AFM engines at any time, from new to 300K+ miles, depending on oil change frequency, driving habits, etc. We see lots of failures on these pages in the GMT900 (Gen IV engines) up to 200K and beyond. I see no reason to believe that the same won't be true of the DFM engines as they use the same lifters and similar actuating mechanisms. In fact, I would wager that the probability of failure is at least 2x that of the AFM engines plus any additional multiplier for switching frequency for each lifter vs the AFM engines. It's likely that lifter failure will be the #1 cause of death for these trucks as they age.
The ONLY way that I would buy one of these trucks new is if someone offers a way to delete the DFM system and replace the collapsible lifters with conventional ones once the warranty is up. I did this in my 2012 6.2 and no longer live in fear. It's great peace of mind.