Noises During Shifting problems of the 2011 Chevrolet Silverado 1500

I purchased vehicle use, with 384 miles. Vehicle transmission became very loud, whining, growling, making clunking noise when shifting; downshifting at times produced runaway shifting, clunking and slipping. Took it to one chev. Dealer and service writer said he had a chev p. U. Just like mine and it didn't make those noises. Went back again and dealer found a service bulletin that applied to my transmission. They ordered parts, installed them, but no change. Went back again and the service shop and they said there was nothing wrong with the transmission and there was nothing more they could do for my p. U. I went to another dealer and they said it needed front and rear planetary gears. Parts were ordered and installed, again no change. Went back to the dealer and they drove my p. U. The service manager said there was nothing wrong with my p. U. ! I spoke with a district specialist at g. M. And she said she would contact the dealership! it is now June 5, 2012 and I again called gm customer assistance and they said the woman who had my case no longer works in that department and they would assign another specialist. She/he would call me today, maybe tomorrow. I told them enough is enough and I wanted another vehicle!.