Hello and thank you for your post. I am a master certified GM tech and can help you to resolve your issue. The hard reverse and hard downshifting is usually due to a faulty valve body regulator valve or a loose connection to an actuator inside the valve body itself. The valve body is the main control center of the transmission that applies the gears and also regulates the oil pressure. If the line pressure actuator is loose or bad then you will have a very hard shift into every gear when the symptom happens (it may come and go) The shift will be so bad that you will swear the windshield will crack.
If the harshness is limited to reverse then your line pressure valve is sticking and the valve body must be replaced.
To determine whether it is an actuator or valve, you will need a scan tool that can turn the actuator on and off while you wiggle the connector on top of the trans. If the actuator turns off and on while you are wiggling the connector then it is a bad connection. If it stays on the whole time then it is probably a bad valve.
If its the valve then you need a whole new valve body assembly. If it is the actuator, then I would replace the actuator (solenoid) and the bus plate that attaches it to the wiring connector.
Hope this helps.
Also, anytime there is a trans repair made, you always need to remove the end cover and replace the input shaft nut as they are very often loose and will cause a delayed shift and or slipping trans.
Hope this helps. Good luck
if you know mechanics then you could probably do this repair but diagnosing it is the tough part. I would see if you can find a place with a GM tech2 scan tool to diagnose it and then attempt the repair yourself or if it makes you feel more comfortable, just bring it to a transmission shop. here is some helpful info
IMPORTANT: One bolt is located in the fender well.
NOTICE: PCM connector bolt torque is critical.
FOR SOLENOID OR BUS PLATE CONNECTOR ONLY see next post
REMOVAL IMPORTANT: Only remove valve body cover. The valve body does not have to be removed from the transaxle to gain access to the solenoids.
IMPORTANT: Using the Saturn Service Stall (SSS ) system, reset the adaptive before driving vehicle if the pressure control solenoid was replaced.
to remove the end cover and replace the input shaft nut follow the steps below and when the cover is off, the left side is the input shaft, the gear will turn as you try to tighten the nut...use a chain wrench to hold it while tightening to 111 ft lb but be sure it is not going to crush the gear. If not sure then use a 1/2" gun to tighten it.
REMOVAL CAUTION: MAKE SURE VEHICLE IS PROPERLY SUPPORTED AND SQUARELY POSITIONED ON HOIST. TO HELP AVOID PERSONAL INJURY, PROVIDE ADDITIONAL SUPPORT TO THE OPPOSITE END OF THE VEHICLE THAT COMPONENTS WILL BE REMOVED.
NOTICE: Before installing wheels remove rust or corrosion from wheel mounting surfaces and brake rotors/drums. Failure to do so can cause wheel lug nuts to loosen in service.