Vehicle Shudder problems of the 1996 Buick Lesabre

I had a previous transmission failure on this car in 1996, after about 12,000 miles. Transmission was replaced under warranty. Current failure occured as I was starting to go up a steep grade. Car shuddered, and engine reved without any increase in speed. There was loss of drive connection between engine and wheels. I downshifted to lower gear manually, and managed to keep car moving forward. After reaching top of grade, I resumed driving in high gear. As I would start on slight upgrades, or try to accelerate speed, engine would rev temporarily without acceleration of car. After stopping on side of road to check transmission fluid, I resumed tranvel. Problem seemed to resolve itself, although there was some "hunting" of the transmission as it upshifted gears. When I returned to home area, I took car into dealership to have problem diagnosed. I have been informed that transmission has failed, planetary gear has broken off and "ground up" transmission. Need to replace transmission. This is second failure of transmission on this vehicle,.