Cutting out at 4,000 rpm

My daughter's 1997 2.4 L Sunfire GT is running better now with new spark plugs but still cuts out at 4,000 rpm. While sitting in the driveway if I slowly ramp it up to 4,000 rpm and hold it, the tachometer drops down to 3,600, then back up, then drops off again, etc etc.

Any ideas?

Throttle Positioning Sensor (TPS)?

Automatic car, right? There may be no problems with the car. If you are sitting in the driveway, that means you are either in park or neutral. If you take it up to 4,000 rpm's you are hitting your rev limiter. If it cutting off while you are driving, then you have some problems. Does it cut off while driving?

No, it doesn't seem to be cutting out while driving. I'm surprised the rev limiter cuts in at 4,000 rpm. Guess I'm used to my BMW e30!

Thanks for the input.

Craig

Did you ever figure this problem out? I'm having the exact same problem in my car now. 97 Sunfire GT, just coming on 200,000 km now. It's a manual, and I can't get it over 4000 RPM. Try as I might. It just won't do it. Started doing this a few weeks ago. Although I do need an oil change, I can't see that being the problem. Any ideas?