My volvo 850 transmition cut out on me. For a

My volvo 850 transmition cut out on me. For a while the arrow on the dash was blinking and it would switch to limp mode. I brought it in to be looked at and they didn't find a problem. Last time it happened the car slipped out of gear and didn't move at all. I had to stop the car and wait a few seconds then start up again. After that, everytime I came to a stop I had to stop the car and restart. What's going on??