the transmission makes loud clunking noise when under acceleration and shifting gears and going up hills it sounds like gears teeth slipping

i have already changed the drivers side half shaft thinking it was that

Obviously, you have wasted some money replacing parts without doing proper diagnosis! Have you checked the left/front transmission mount? We need a better description of the symptoms in order to help! "it sounds like gears teeth slipping" is not sufficient info.

Not a big deal, but for future references, "92 Buick Lesabre" is not a question.
Especially in a "Buick Lesabre" Forum.

Chris.