Hello, if you are using either of the two March released drivers (21.3.1 or 21.3.2) roll back to the last Feb driver (21.2.3), the March drivers are not very good for VR.
Otherwise, I would suggest lowering your SteamVR SS to 100% and see if that helps and then increasing it by 10% each time until performance starts to degrade.
Regards: Jack