Do yourself a favor and start with getting the codes read. It is a pain to do it manually, find a shop or dealer. I had a 90 that slipped on O/D and a trans shop told me I needed a new unit. I flushed and was about to get into checking the shift solenoids. I ran the codes and had a few. I have seen that before pointing to a bad module. I found a used one and boom, shifted like new. Car had 180k and was still going with oem trans.
Would this explain reverse not working as well?