95 sunfire, transmission problem?

I have a '95 sunfire with a 2.3 automatic.
I will be driving at a steady speed in overdrive and it will start jumping .5 rpm, feels like it wants to down shift. I can put it into 3rd gear and there is no problem. I have changed the torque converter solenoid and it is still doing it. Any one have this problem or know what I should try next? Or am I looking in the wrong place, could it be a vacuum problem?

Thanks!

A misfire under load in lock up can do this, this can be better determined by having it scanned with a trans capable scanner for trans codes and check for tcc slippage. If ok I would suspect a lean misfire or a plug/wire condition.

If the jumping is kinda rythmic, then I would suspect a misfire but only if it did it all the time whether traveling or stopped. Otherwise, have codes read if you can.

you should be able to get the codes read, but it may be a dealer thing. the 2.3L ATX is OBDII so autozone MIGHT be able to get you the ecm codes, but I'm not sure about the tranny codes.

Only does it in overdrive, no problems in other gears or during idle. My dad has a scanner from snap-on that we are going to try this weekend, but he said if there are no lights coming on in the dash then it probably won't throw a code. So that is why I have not put it on the scanner yet. Thanks for your comments, hopefully we will figure it out this weekend! Any other suggestions are welcome.