2001 Cavalier rpm fluctuation on the highway
 

Recently bought a 2001 chevy cavalier (automatic) for my gf as a replacement car for her 1996 sunfire. After getting it all saftied, e-tested, and the like; took it for a drive. Runs good...did a full tune up on it, plugs, air filter, oil, didn't need wires. While driving down the highway at about 60 mph, I noticed the rpm fluctuating a little. About 125-250 rpm. It almost seems to me that the torque converter lock-up clutch is slipping a bit. If I hold the throttle steady and don't move it at all, the rpm's sit fine. If I slowly roll into it it seems to hold rpms with speed (much like a standard would). The problem is, if I ever so slightly back off, the rpms pop up about 125-250. If I roll into it more then it seems to set into 4th gear (rpms up about 1000 from Tq conv lock up rpm) I know alot of cars disengage the Tq conv on decel or down larger grades, but I am talking about driving on flat and making a very minor and gradual speed change. It's not like anything I have seen before. I am wondering if it could be an issue internally with the transmisson, Throttle position sensor, or just merely dirty fluid. The car has 215,000 kms (134,000 miles) on it and I have NO CLUE in what state the trans fluid is in. I think I am going to change it, but I have no idea what GM uses for transmission fluid in those cars. Dexron 3 or 4 (whatever they are up to now) good enough?

Any ideas would be great. I am not well versed in diagnosing domestic cars, only ever really worked on asian stuff.

Did you ever get a response or solve this problem? My daughters car has the same problem.
Thanks,
Ron

no never did. I am going to look into it soon though. I have been reading up a little bit about the cavalier transmissions and apparently it is possible that there is shavings in the valve body of the transmission from the machining process when the trans was made. When I do figure it out though I will definately post the solution.

I also did a fluid change change but not the filter. I am going to change the filter when I do look firther into the problem; and obviously new fluid will be going in again also. But since the new fluid, the trans still has the problem.

My solution
 

I found a slow leak in one of the cooler lines that caused a low fluid level.
After changing the lines and bringing the fluid level up to the proper level, the problem went away.