I take it that since you are posting in Buick you are referring to your 93 Pk Ave?
Often the solenoids, valve body check balls etc...get gum & varnish build up, causing slipping or No lock up. Good transmission maintenance fluid & filter (once every 35k miles) goes a long ways in keeping transmissions healthy.
Before I would replace anything, I would put a full can of this into your transmission fluid, drive it for about 500 miles and see if it improves.
Trans Tune - Sea Foam Sales Company
There generally as far as I know are 2+ solenoids. I would want to refer to the FSM for your vehicle.
On my 4t65-e I used the Trans Tune, things got better fairly quickly, it was harsh shifting when hot only, and lessened once Trans Tune was in.
I then also installed a Transgo spring & spacer shift kit into the accumulator body accessible for the pan drop area, and replaced the filter and went to the best GM trans fluid Dexron VI (6) Nice stuff!