My recent experience as an GMC owner has been horrible. I have a 2016 GMC Sierra with 51k miles that is less than 1 month out of warranty. Last week one of the lifters stuck and is causing cylinder #7 to misfire. Local dealership SouthtowneGM originally said it would cost $90 to diagnose. They call back a couple hours later and now need $400 more just to determine the issue. A GMC representative tells me a dealership must diagnose the issue before they can determine if they can provide assistance. It's ridiculous that I have to pay a dealership $500 dollars for them to tell me what I already know. I had a local certified mechanic diagnose for FREE. Its a stuck lifter!! Caused by the AFM. Common Issue. GMC will not even tell me if there is a chance if they may be able to help me out without making the $500 gamble. For something a certified mechanic has already diagnosed. I will be heading to the Toyota dealership this weekend in a 2016 GMC with 51K miles firing on 7 cylinders.