'90 Dodge Spirit tranny problems

Just bought a '90 Spirit ES with 58,000 miles. Got it from a Dodge dealer who fully serviced the car and has since it was new. Car has been taken care of and seems to be in perfect condition. Ran great for the first two weeks. Now it is shifting erratically. Will downshift for almost no reason at highway speeds. Just going up a slight rise or gently pressing down on the gas will cause it. Everything else seems normal. I don't know how to tell if it is the 3 or 4 speed auto. It has the 3.0L V-6. Any help would be appreciated.

i have a shadow it just about the same besides the body style anyway my car had some trans problems changed the fluid it was better. also to find out if u have 3 or 4 speed look it up on i think autozone's website

a bad speed sensor will cause crazy shifting and rpms, makes it seem like a tranny problem, I know on the 3.3 the speed sensor is located on the tail stock of transmision. It should also throw a code but does not always turn the check engine light on

On the 3-speed transmission, the speed sensor is a a throttle cable coming from the gas pedal to the transmission. This cable can fall off its mount.