Transmission Gear Slipping problems of the 1998 Chevrolet K1500

I drove on the highway aprox. 20 miles. When I came to my exit and stopped and tried to go my transmission slipped causing my to roll out into traffic and pause briefly till it slammed into gear. When I got to a spot I could pull over and check it out I realized no reverse. It would not shift out of first also. I called gm to report since the transmission had already been replaced once under extended warranty. I was told to take it to gm dealer for diagnosis. I was told it needed replaced or rebuilt. I got a second opinion from r and r transmission. They explained the transmission needed an update to work properly and this is probably why the first one failed. They rebuilt transmission. This near miss could have been serious.