Transmission

Hi everybody I'm new here. I just bought a 93 grand prix se. It has a 3.1 v6 auto transmission. The problem is when I was driving on the highway today and was just cruising along(not with cruise control) It felt like the transmission slipped if this is possible. I mean that the speed was like fluctuating a little. It only did it for a little bit but It got me nervous. I was curious if there is a known problem with this car with this happening? Not sure if you need this info, the car has 140,000 mls on it. Thanks in advance if you can answer me. Have a Merry Christmas

I have a 93 Z-34 and with the old transaxle used to do that. After a while it went north and I had to replace it. COuld be the sign of a problem to come