I changed my filter and about 4 quarts then about 2 months later drained another 4 quarts. I used Amsoil recomended ATF. About every 5000 miles I will do another drain and fill 3 more times. That should have the majority of the fluid replaces with Amsoil.
A lot of people have recomended the drain and fill process instead of flushing.
I have 175k on mine and I do not know how much care the fluid got before I got it with 150k. It was a commuter vehicle if that makes a difference.