I would imagine that is because the twin pass does not have a heat exchanger for the auto box. All you'd have to do is run a seperate transmission cooler.
You can have a twin pass on an auto......>> It just means you will have to run a remote cooler and not one in the side tank of the radiator. Since a remote cooler on an auto is just about a "must do mod" then it isn't an issue. If you fit a twin pass radiator to a manual and then at a later date change the car to auto then you keep the radiator and fit a cooler, simple.:thumbsup: