I have a 1996 Olds. It wont go into gear until the car has been started for about 4 min and setting in gear. Then it’s good for the rest of the day.
Is the trans fluid level where it should be?
If the fluid level is ok, I would suspect a bad oil pump in the trans.
Provided you have the correct amount of tranny fluid I’d guess you either have a valve body problem or more likely a failing transmission pressure pump.
Your best course of action is take it to a tranny specialist for diagnostic testing.
Either way, I’d say you will be looking for a replacement tranny fairly soon.