How do you flush the transmission fluid?
The way I do it is disconnect the trans fluid cooler lines at the radiator; collect the fluid while briefly running the engine (you will pump out about 2 quarts). Save all fluid removed so it can be accurately measured, because you should replace exactly the quantity you removed. Add fluid through the fill hole accessed by removing the red plug on top driver's side of trans near the air cleaner. Repeat the brief running and collecting until you have flushed 10 or 12 quarts. If you want to make sure the fluid level is exactly right on a Malibu, you need to go underneath and remove a plug there and fill until it runs out with trans at operating temp. I omitted this step since no leaks had occurred and I had the car since new, and accurately measured the amount pumped out and replaced with the same amount.