Suspension Noise problems of the 2012 Chevrolet Silverado

I have been having problems with my chevy Silverado truck, texas edition, it has 23,800 miles on it I purchased it with o miles, I adhere to oil changes and any repairs in timely manner. My truck has been in service department twice for the same issue, when the transmission is switching gears, it makes a clunking noise while driving it, it feels like someone is bumping the rear of truck. The repairs include transmission hard shifting 2 - 3 times, rr upper control valve body and spacer plate replaced, reset transmission, 1 2 3 4 clutch regulator valve binding in bore. Also replaced springs, second service the u joints anitsd yoke replaced, my truck continues with same problem, please look in to this its horrible & very dissapointing why can`t they fix it, my truck sounds like an old vehicle I think something is wrong with suspension. I`m desperate to find an answer. Its an expensive truck to be dealing with these issues.