1999 Saturn SL2 Auto transmission bangs

So you have a delay bang into reverse and when the car down shift's it bang's?What code's do you have in the computer?

I don't know computer codes since I don't have tool to read codes. Is there a way I can check codes without buying $200 tool?
I replaced transmission fluid and filter, and cleaned sticking throttle and the shifting is much improved.
I will have to wait for cold weather to see if new thermostat and cooling system service fixed problem with no high gear when cold.

Most likely you have a pressure issue inside the transmission And possibley a loose input shaft nut.I would first remove the transmission side cover and see if the input shaf nut was loose real common for that year and model.That's the only way to see if it's loose.Then when the fluid was hot I would check the min and max pressure of the transmission.Then I would remove the valve body and air check the clutches to make sure all the pistons were good.As far as getting codes if you live California your out of luck but other states you can go to a auto parts store like auto zone and they will read the codes for free.Let me know what you find out.