auto transmission click sound on 2002 Chevrolet Avalanche 2500

Hi I have avalanche 2002 2500 8.1 ... the auto transmission when change from gear to gear( from 3 gear to 4 gear ) i hear strong hit ( click ) ... what is the problem ?? Thanks

Possibly the rear u-joint is worn out and will click or clunk when shifting, you can locate a shop here and check prices here