My truck's transmission Has issues too. On a 2015 Sierra 2015 slt, 45000 miles. One big clunk noise from underneath and now no more power. Engine light on, d-light blinks, manual doesn't lock in, but vehicle moves, backupcamera doesn't turn on in Reverse. Reader says transmission issue with power loss. for some reason these trucks don't seem to last anymore. Pretty disappointed. Last truck was a complete fail, had to sell it back this one goes to shit after 45000 miles.........