I had the same issue with my 2016 MX. It was an extremely unpleasant ride. To the extent that I constanty got headaches and neck pain while and after I was driving it. Anybody sitting in the car noticed it immediately how stiff and uncomfortable it was. I tried to change tires, lower pressure, but nothing really helped.
Now, after a few months of research I found Tesla made a suspension upgrade on October 18, 2016. So I decided to do what they did. Swapped all 4 air springs to newer MX 2.0 versions (front 1027361-25-E and 1027361-00-E replaced to 1027361-00-G, rears to 1027461-00-G, previously were 1027461-00-E), and also replaced front and rear stabilisators (original sway bar on the front was 1027381-99-G, which looks like a stick, new part is 1027381-00-K, much more springy, for the rear it was originally 1027481-00-E but replaced to the revised 1027481-00-H). Now, believe it or not, it drives like a dream!
As always, do it on your own risk. Sway bar replacement part needs the HV battery to be taken down for a brief moment.