1994 Chevy Cavalier, 89 K, 2.2L i think, AUTOMATIC

I got a tune-up yesterday and engine sounds great. Driving home the car seemed to be running better than ever until the day after when I noticed it is now not wanting to go from second to third gear without some effort - first to second is no problem.

The person who did the tune-up said this couldn't have anything to do with the tune-up and that it sounded like a transmission issue??

I checked the trans fluid and it looks just fine (level and color).

any suggestions?

thanks.
Bobby