I'm sorry to hear this about your Denali.
I had to search non-AFM VVT cam/lifter to learn more about your issue.
Hopefully, you can your get your questions answered here on this board, but you may have to find a different discussion board.
With my limited mechanical skills, it seems that a valve job is needed on that one head.
Perhaps both heads should be serviced?
And then consider selling the vehicle.
My poor at best mechanical skills allows me to service and maintain my 1979 Wagoneer. It is nothing more than a hobby.