Hardly noticed vibration at first. Then became more noticeable. Eventually started banging into gear. Made appointment with service (Crystal Auto, Homosassa, Florida) . Told by advisor Chevy is aware of problem. They put wrong transmission fluid into vehicles. Included ALL 8 speed auto transmissions. Dealership unable to flush out fluid untill they get the KIT to make repair. A wasted trip. Now engine light is on. I will leave truck at dealer and try for a loaner vehicle. Truck in not safe to operate. I feel all the vibration will cause the cast casing on the transmission to crack. Dealership said driving it is OK. Not their truck. Shame on GM. Wonder if my first payment will be due while truck in in the shop. Will advise if/when repairs are made.

Update from Jan 27, 2019: 1-27-19. Truck still at dealer. Service called and stated the KIT is not in yet. First payment is due soon. They did give me a loaner truck. It has a six speed transmission that seems to be fine with about 500 miles on it. Update will follow.