1994 Chevy Cavalier Help me please!

I am the owner of a chevy cavalier. I love this car and I do not want to replace it. It seems like when I travel on the highway or a long road for 15 mins or more, it will stall out when I down shift. I looked it up online and alot of people are saying to unplug a sensor to the trasmission. A sensor was unpluged when I bought the car and when I plug it in nothing happened intill recently. I really depend on this car because I work full time and goto school full time. ALso when I looked up different transmission sensors there was like 5 different types and some say u need to replace it under the valves some say on the side of the valve and some just suggest buying twenty different books to find the problem. Please save my nerves! Thanks!