Non-AFM doesn’t eliminate the risk of lifter failure, just greatly reduces it. Back in 2010, I bought our 2007 Denali XL with 100K from my work. No AFM either. It had been maintained well as the guy at work responsible for taking care of it was very particular about vehicles. There was showroom ready and then there was Steve Doud ready. Come 150K, and I was in the same boat as you. Loud knock, wouldn’t run. Dealer said it was likely a lifter failure and found metal in the pan. Put in a GM reman with 100K warranty. Fast forward to 272K, and I get a nasty noise in the motor that sounded like a lifter had gone bad. I tore it down myself because I wasn’t going to put another motor in at 272K. Found that the roller on the #5 intake lifter had locked up and was scrubbing the cam. No metal in the pan or filter. Was able to swap out the cam, replace the lifters and all the associated parts and drive it for 25K more miles and traded it.
I’m not trying to add to your worries. My point is, any vehicle, no matter how well they are taken care of, can have stuff like this happen. Stop kicking yourself. You took the steps needed to try and avoid this, and life happened.
