Does the factory recommend the use of a weight distrubuting device on the E53s that have rear self leveling suspensions? I would like to tow 5,500 lbs., which is close to the max towing limit, but over the recommended 80% of max tow rating. I have a factory hitch. I have heard not to use a weight distrubuting hitch on the unibody X5, and/or with the self leveling suspension.