My '02 X5 4.4 with 115kmi has newer struts, shocks & rubber. The rear air suspension works and without fault codes. However, bumps have been getting rougher and rougher where the car almost bucks in the back when I go over a bump on the highway. What is causing the stiffness? Last checked, the ride height was fine, airbags were not leaking, and tire pressure was fine. Since there's no rear coil springs, what would cause this?

Thank You,

X5Guy70