Go through your WDH setup procedure again on as flat and level a place as you can find.
Sway is usually associated with TT tongue light, tail heavy. Try moving some of the trailer load forward of the axle.
I always pump my TV tires up near maximum sidewall marked pressure when towing. It stiffens the sidewalks for less flex. While the door frame placard from the factory states the recommended pressure for the maximum load, it is also a trade off for passenger comfort. IMO, passenger physical comfort ranks well below driver towing comfort.
You added sway control bars? Those are friction controlled and the friction is manually adjustable.