IMO a cooler is masking the core problem in normal driving circumstances.

The transmission cooling is designed for the optimum operating temperature range for the transmission. If the temperature is varying beyond specifications there is something not working properly in the existing components.

The exception can be if one is towing a lot or beyond the maximum towing wt. or repeating drag racing starts without letting the fluid cool. If I recall correctly the max temp. spec. for the 5HP24 is 200 degrees. If the transmission temp is above that during normal driving something is not working properly.

I notice you were towing. Was that the case prior to the cooler?

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X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior
Dallas