Guys! This is a TRUCK! I don't get why everyone is so picky on this clunking thing! GM is the same manufacturer which makes Cadillac and smaller Chevy and GMC cars over 100 years, without clunking, the same as Ford. Now both GM and Ford are using the same transmissions. They both know how to make cars and their transmissions. They are not stupid to make durable trucks breaking fast. This clunking thing has been with these trucks in almost all past generations with automatic transmissions, when changed to 6-speed. It's very simple. These trucks have naturally aspirated 8 cylinder engines which oxygen intake depends solely on atmospheric pressure and does not rely on forced induction through a turbocharger or a supercharger. Therefore, they drop the rpm very fast when they come to stop. Also, the flywheel in these engines is very light compare to 4 or 6 cylinder engines. They have the flywheel just to engage the starter. Therefore, there is less inertia being saved in them when the car comes to stop in low speed in very low rpm. On the other side, all truck's inertia is transferring to the transmission from the rear end. During synchronization between the transmission and the engine in very low speeds, specially coming to stop, sometimes such clunking condition happens. It's getting better after couple of thousands miles when the computer learns your driving style, but it will never go away completely. This is my 4th Silverado. None of my past silverados (past 3 generations) had ever had any transmission issue because of clunking.
By the way, this thread is for backup camera not for transmission clunking. They are other related threads that people are talking about it more in details.