we have bought a 2001 olds alera runs great,the problem is the transaxle wants to shift down from overdrive at around 65 mph but when it goes to 3rd it will try to go back to overdrive , it goes back and forth causing the car to jerk untill you speed up or slow down ,i am going to change the fluid and filter,this car has a solenoid on the transaxle but could it be causing this,i am not to sure if it controls the overdrive,the fluid is not low thier our no leaks ,the car has about 73000. on it the motor is a 2.4 liter