2004 Buick Limited Automatic Level Control

One morning I start my car and drove through the road as usual. I was surprised but it rides like a old car. It seems there was something in the trunk and I feel each bump. I went to the garage and I asked them to take a ride with the car. They take a ride with the car and they said it doesn't ride like a Buick for sure. They looked under the car and they said that the automatic level control was jammed. They told me they are going to put that on the computer to analyse the problem. They can't do nothing and the car was still riding bad. They told me to order a new automatic level control. I told them to order two air shocks to put with the automatic air control. The work was done and it happens again today. If I ride the car for a long time; it comes to normal. What's the problem? If I want to sell that car; it seems to be a major problem. I wait for your answer. Thank you in advance.