I had a similar issue with my 04 over a year ago. Turned out it was the switch on the console that sets the height adjustment. It was "thinking" that the car was in something other than neutral while driving, so kept adjusting the rear as we were driving. It felt like I was riding a horse trying to throw me. The dealer replaced the switch, and that completely solved the issue. It was not cheap, and not covered by the extended warranty because the switch is defined as an expendable part. But, it was sure nice to get the smooth ride back. Hope this helps!