Extremely rough ride on 2007 cadillac dts . seems to be the read end that is riding rough.
Does the vehicle have the Magneride suspension system?
It is possible, magnaride or not, that the air shocks on the car have failed and the airbags are jammed up. Or magneride could have failed. Any good auto shop should be able to fix it.
How long has it been doing this? How long have you owned it? Did anyone put air in your tires recently?