RPM Jump in 4th?

Hello every one.

This is my first post, so I probly should introduce myself. My name is Ben Paprocki and I own a '92 silver LSi. So far I love the car, it handles great in the winter, and is fun to drive on summer days. I get a lot of questions about the car because there are so few of them in my area (Milwaukee).

Any way, on to my problem. I have been reading through everyone's posts and can't seem to find any that pertain to my problem. I have noticed that when I am driving on the freeway, at around 75 mph, the rpm will jump around. It usally settles at 2500, but when I get to a small hilll, or a long streigh it will jump up to almost 3000. It doesnt seem to do it at every hill or in any pattern. I dont think it is the tranmission sliping (at least I hope not). I think it may be a sensor, such as the TPS, but I wanted other peoples opions before I go tearing into the engine. The car has almost 130K on it, I just replaced about 6 qt. of tranny fluid (non-synthetic).

If anyone has ideas please let me know.

Thanks a lot!