At anytime the service engine yellow light will come on and there will start to be a hard trans upshift and actually down shift. Service engine light on also and parts place says lean bank 1 and 2, O2 sensors they say. Do the sensors also cause the system to go to a hard up and down shift or is it a transmission problem. Saturn does not give dipstick to check fluid levels. 2001 L300 with 90,000 miles.
The o2 sensor codes are not causing the transmission issues. I would have the codes read again but this time, have them read while the light is on and the harsh shifting is occuring. What your transmission is doing is going into limp mode. When the computer detects a problem involving the transmission, it sets a code, maxes out the line pressure to protect the transmission, and fixes the transmission to 2nd gear (3rd gear in some vehicles). It sounds like you are in limp mode. I would either wait until the harsh shifting returns and have it scanned immediately or go have a shop use a real scanner on it and look for history codes. This might give you some indication. Post back when you have more info and we will go from there. We will figure this out.
transman
Have you had the tranmission fluid and filter (if accessible( changed within the last two, three years? If not, you should start there. Usually, only a fluid change, and not a (wallet) flush is needed. This could help (and it’s cheap).