Picked up a 11 Denali with approx 130k on her. She’s knocking but I’m not convinced it needs a motor, did a little digging and found rocker in cyl 7 with no movement. Being that I don’t know a lot of history on it should I attempt to get that lifter to unstick and hope it works or tear it apart and see what the damage is. Seen a lot of different videos where something as simple as marvel mystery oil getting the lifters back in working order as long as it’s not far gone. I figured if it needs a motor then so be it, after all the truck didn’t cost me anything.