As Jorn says but the interval I run out to is 40k to 50k miles.

I would drop the pan/filter and then position the torque converter with the drain on the bottom and drain it too. It takes a while to drain the TC. You should find a magnet in the pan that will need to be cleaned off. Don't be alarmed by the debris on the magnet.

I would not as much "flush" it as drain everything and refill.

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Jim