50K miles, original transmission - replaced fluid with OEM recommended Dex II. Weeks later the electronic automatic transmission "hunts" in 2, 3, and 4th gear. By hunting, the rpm cycles up and down about 100 rpm with constant throttle. No OBD codes.
Transmission hunting problem on 1999 Oldsmobile Cutlass
Did you remove the oil pan when you changed the fluid? Was there any debris in the oil pan or filter? You said you changed the fluid. I don't like using flushing machines on older transmissions as sometimes debris gets dislodged and causes problems afterward. Just drain and refill with pan removal is the best way to service the transmission.