When you do a flush using the engine as a pump, do not pump out more than 2 quarts at a time. If you start to see air bubbles, you can damage the pump.

With all of the mileage on your car, I suggest the dump and run method as it is easiest on the tranny. You could check the level of the ATF prior to the dump, mark the dipstick as the level will appear much too high on a cold/not running car, then refill to the same level.

I doesn't matter who's brand of ATF you use, it just has to be 3309 compliant.