If you have not thoroughly checked the rest of the suspension including the front axles and sway bar links/mounting bushings, I would do so. Even though you have done some suspension work I still lean toward cause is in the suspension. Sounds pretty bad since you can't drive it on the highway now. How many miles on the suspension?

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