Originally Posted by upallnight

The reason why the temperature is so important is because ATF expands with heat, so the hotter the fluid is, the more it has expanded. Don't make the mistake of draining a hot trans because unlike an engine only 60% of the fluid is in the pan. The rest of the fluid is in the Torque converter and if the fluid in the torque converter is hot it will upset the actual amount that you put back into the trans.

I would drain the fluid from the pan and let the car sit over night. Next morning I would pump ATF into the trans until it come out the fill hole. Put the plug back into the fill hole and start the engine. Go through all the gears and pause in each gear with the engine running and put it in neutral, remove the fill plug and with the engine still running pump ATF into the trans until it starts to come out the fill hole. Put the plug back in and call it a day.