Hi Scotty, I have an 09 GMC Sierra Denali with 6.2 non afm with 6 spd. It has just under 138k on motor, it runs strong with good oil pressure and no engine light or codes. Having what has been diagnosed by couple local mechanics, one indicates lifter is going bad and the other one I recently talked to says it's probably wrist pin. Not sure if that is the piston or lifter he referred to. The noise doesn't constantly tap loud while idling, sounds similar to a diesel when driving it tho. The noise is louder when motor is cold. I've used a couple additives when I thought it was a lifter getting stuck but didn't help after a few months of doing that and changing oil. I was told it will be ok for awhile but I just don't want to be out a motor trusting that it will be. Any advice? thank you