Had a slight vibration issue at higher speeds on my 2018 SH-AWD that I never had on my 2015 V6 Tech TLX. Read several threads here and was convince it was the tires or axles. Long story short, after I turned off the RDM road departure mitigation which also supplies steering input, the vibration is gone. So it turns out my vibration was caused by the RDM being too sensitive and giving steering input. I thought I had the steering input off as my LKAS was turned off but didn’t realize RDM has steering input. The 2015 Tech models did not have RDM which explains why I never had any vibration in my 2015.

RDM is turned off by a long press of the RDM button which is to the left of the steering wheel on the dash. Once off, it stays off during restart and the display states RDM off each time you start the vehicle.

Odd. Reading this forum it seams like everyone has a vibration issue. No one I know has one either. My issue was from the RDM on certain roads at high speeds. As soon as I turned it off no more vibration. The steering set up is very different with the electronic safety features and the corrective actions it was taking caused a feeling of vibration when it was jiggling the wheel.