1994 Chrysler Grand Voyager

Transmission problem
1994 Chrysler Grand Voyager 6 cyl Front Wheel Drive Automatic 204500 miles

i was hoping some one could tell me what is wrong with my transmission. I have a 1994 crysler grand voyager 6 cylinder 3.3liter. My transmission slips into low gear when I reach between 20 and 25 mphs while in overdrive and does not change until I disconnect the negative cable. But even after reconnecting the negative cable the transmission slips back into low gear between 20 and 25. I have changed my transmission oil and filter but there is no change. I was wondering if my transmission is bad or a cpu unit for my transmission
May 17, 2009.

Has the check engine light come on? It could be a vehicle speed sensor (VSS) that is causing the problem. Have you had the computer scanned for codes? Most parts stores will do it for free, so there is no money out of pocket. Have that done and let me know what you find.