Hi,
I have a 94 Grand Caravan with 3.3 l / a604 transmission. The transmission has nearly 100k miles on it and I've taken very good care of it. It shifts very well in dry weather. However, after driving in the rain for a while, it will begin to give a rough bump shift when slowing down, right before I come to a stop. This only occurs after driving in the rain for a while - I actually got the same problem after taking the car through a car wash once. My guess is that some wiring is being affected by moisture, but I don't see anything obvious under the hood. Was hoping someone may have some advice. Thanks.

You could spend some bucks at a shop where they can check for any transmission specific codes with a transmission scanner to narrow down the problem or you could spend some time inspecting the sensor connections on the front of the transmission for security, corrosion, or contact damage. When reconnecting coat the edges with dielectric grease to help seal them.