Today, I had my indy put in amost 8 quarts (empty about 8.8 quarts) of Mobil synthetic atf with a new filter kit. They drained and cleaned both pans and blew air through the oil cooler lines to remove as much of the old fluid as possible. They left the old atf in the torque converter as there is no drain. Note, they did not flush, they drained.

BTW, the trany had been serviced about 31,000 miles ago. While I did not notice a problem before the change, It seems as if the trany now shifts smoother and has a bit more pep off the line.