My 2002 Alero with the 4 cylinder ecotech engine will periodically downshift after engine warmed up at aproximately 5 miles pf highway driving (usually 65-70 mph)while on cruise and engine temp is normal.
The terrain is flat and it doesn't matter if the air conditioner is on or not.
The rpms will fluctuate between 2500 and 2900 when doing this.
Is this normal or do I have a problem. The vehicle is under full warranty.

Its sounds like something funky with the torque converter is going on. At highway speeds, if you give it just a little bit of gas, the torque converter will unlock, boosting RPM's just a bit and give you a little more power. Only if you give it a lot of gas will the converter unlock and give a full downshift.

Since your car is only jumping in RPM's slightly, I would say there is your issue. Since its under warranty still, take 'er in and see what they say.

Jeremy

Well I finally found the time to take the car in and have it checked out.I had them change the oil at the same time since it was soon due.
It down and upshifted all the way there but when they took it for a drive (14 miles round trip,twice!) they could not duplicate the problem.
I couldn't believe that it would not display the same symptoms when the mechanic drove it but I found that it stayed locked up for me the remainder of the summer and now suddenly it's doing it again,constantly.
I am going to try to get it back to the dealer next week but would appreciate hearing any further opinions or experiences on this matter.
Thanks in advance.

If it doesn't do this when your not using cruise, I'd say the cruise control servo might be goofy to where it is not settling on a constant throttle position to maintain speed. If it is opening and closing the throttle when it shouldn't, this could make the computer decide to slip the TCC more or less.

For those of you that may be having the same problem they finally got it figured out at the dealership. The thermostat was malfunctioning and letting the coolant temperature drop which in turned caused the torque converter to unlock causing the unnecessary and constant downshifting at highway speeds.

Thanks for updating your post. It's odd though that the failing thermostat didn't set off the S.E.S. light.

Glad you got it figured out.

- Jeremy