I did a 100% fluid change in mine. I have a front trans cooler. Pull the return line and fill the bucket two quarts at a time. Start engine, drain two quarts. Turn off engine. Put two quarts in. Start engine -repeat.
This is it on the newer Toyota trucks. Only other thing is that there is a thermostat that needs to be open to route fluid to the cooler. It is possible to jump this with a short wire to make it stay open during the servicing.
