Re: Car tilts to the left when parked
My car is currently in for service on an issue much like this - assuming you also have Quadra-Lift.
I had several "Immediate Air Suspension Service/Repair Required" warnings pop up on the dashboard, and took the car in for service. They replaced the control module for the suspension system and declared it fixed, yet the warning came back on about a week later. I've taken it in again, and they have written to Detroit on how to fix the issue. If you Google it, you can find several others with similar issues.
However, with how it relates to your problem - my dealer told me that yesterday when they came in the car suspension had raised on the back right wheel although they had left it at normal ride height. Definitely an issue.
Assuming you also have Quadra-Lift, it might be a similar issue.
Check it out with your dealer and see if they can find any error codes associated with the air suspension.