rides very hard & rough on 1999 Cadillac DeVille

when hit a little rough spot of road back end wants to fishtail

Asked by for the 1999 Cadillac DeVille
you probably have air ride suspension ,check for air leaks and air pump operation
Yes it Has Automatic load leveling ,pump working & no leaks,yet feels like shocks are full but the car is the same level all the time. when on expressway the back axle when going over the expansion cracks are very very noticeable