Mike L. will probably chime in, but what I usually do is change my tranny filter with my oil. (about every 8500 miles) It is cheap insurance on an expensive tranny. I filled my filter with tranny fluid and put it on. Don't forget to take the magnet off the old filter and put it on the new one. I believe the recommendation is to change the filter every 10,000 miles and fluid every 25,000. I don't have my owner's manual in front of me, but obviously it depends on the environment that you are operating the vehicle in too.