Your DeVille should have ELC- Electronic Level Control. Rear air shocks and a small compressor probably located by the right rear wheel. If you want to see if its working turn the key 'on' with the engine and anything else that makes noise (like your new CD player) off. Open the trunk, sit on the edge of the trunk lip facing backwards and pick your feet up. Wait 10-20 seconds and you should hear the compressor kick off and feel the car slowly level up.