Transmission, 1992 Volvo 240 DL

I have a 1992 Volvo 240 DL wagon. The last few weeks every once in a while it would feel like the car wasn’t shifting from second into third gear. This is an automatic transmission and it seemed to happen if the car was warm or cold but would stop after just a few minutes. Then today I got off of the freeway after 30 min. or so at around 65 mph and it started again. This time it lasted for longer than ever before. I checked the fluid and it looks full. What do I do about this ? Is my transmission shot? I love my car and would hate for this to be the end of what has been a beautiful friendship. Thank you.

The transmission fluid may be “full,” but when was the last time it was changed?

I’m not 100% sure. I had some work done in December when I was recovering from surgery. As you can understand I am a little foggy on the details of what was done due to the pain meds.