I just bought a '98 V90 w/183Kmi. this last winter. It demonstrated the same symptoms. I flushed the somewhat dirty Mobil 1 (according to previous owner) fluid and replaced it with AMSOIL synthetic. It seemed to improve the shifting somewhat but still somewhat harsh and erratic. A few months later I got a check engine light with flashing W-E transmission mode lights. My indy mechanic reset the error and ordered a PNP (neutral safety switch). It ran OK for a couple of weeks and came up with the CEL again. He replaced the PNP switch and the missing air guide (under front lip spoiler) at the same time. This cleared up the CEL and the shifting is now much smoother and less erratic. In your case I would suggest cleaning the electrical connector to the transmission 1st this may be beneficial.
Good Luck,
Tom Heitzman