Speed Sensor problems of the 2002 Chrysler Town & Country

My 2002 town and country had to have a new transmission in 11/12. In June of this year, my speedometer quit working causing the transmission to shift hard. I took it to the transmission guy who replaced the speed sensor. It worked fine for a couple of weeks. Then my battery light came on suddenly. I had my battery checked and they said it was fine. They said I might need a new alternator. So I had a new alternator put in. The car did ok for about a couple of weeks, then the speedometer started jumping erratically. I took back to my transmission guy who said the speed sensor was fine. He thinks it may be due to a loose wire or a possibly damaged wire or corrosion. So far, no answers and my car is still undrivable. It jumps when I am stopped. It acts like its already in second gear or something. I am afraid to try to drive it as it is dangerous. Help! I can not afford to put more money into this. It cost too much to start with. 3. 8l v6 limited. I am a single mom with a child who has heart defects. I need reliable transportation!.