I agree that it does sound like the torque convertor and also to take it to a recommended transmission shop for diagnosis. More often than not once there are symptoms such as you are experiencing a fluid change will not fix the problem. Since it might not fix the problem, that is the reason to have it checked out by a qualified tech first.

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