Does your XT6 have a hitch reciever and 7 prong harness from the factory? Asking because we were told ours did and when we checked it did not but my wife also has the smart tow and upgraded engine components.
A weight distribution hitch is recommended to relieve stress on the rear of the vehicle by helping spread the weight through the vehicle to the front. It does not increase the towing capacity of the hitch reciever or the vehicle itself. The reciever will still be rated for usually 4500lbs and the tongue weight for between 400-650 depending on the reciever you have. That being said if you have an aftermarket receiver I would not push that at all. If Cadillac has any indication of towing and you have an engine, transmission, or suspension issue they can void your warranty coverage.