I have a base model 2005 Deville that I have recently acquired. The car is in great mechanical shape but I have questioned the suspension on it. When I first start the car I hear the suspension in the back doing its thing, but I have noticed that when there are people in the back or the trunk is full the car sags. Shouldn't the ride height remain the same no matter what? I guess I am comparing it to a Lincoln Town Car air suspension, are they the same or different? Any info is appreciated. Thank you.