2006 STS4 rear suspension
 

Having spent 15 years in Blazers, I finally got my first Cadillac....2006 STS4. I chose STS because I wanted a GM car, but I also wanted AWD. I love almost everything about it, but i'm not liking the ride when there's an adult passenger or two in the back seat. It seems to handle somewhat mushy and bottoms out. Is this a standard trait of the STS or cars in general or should I take it in for a check? I highly doubt owners of the top of the line would put up with this, but mine is the cheap one... talk about an oxi-moron.... STS/cheap... anyway, i mention this because the basic model might not have something the higher level models have. Any thoughts?