[Signman]

One thing that helped my sway issues was to measure the front and back of the trailer when loaded and connected to the tow vehicle on a level surface. The front should be an inch to 1.5" higher in the front.

You can ad a friction type sway control to get even more control if you don't want to invest in the model suggested.

A way to get rid of 95% of the sway is with a dually. A lot of sway is eliminated with all that rubber.
When towing if you are one lane from the Jersey barrier when being passed the wind pressure is amplified plus those SUVs push a lot of air almost as much as the block busses and tractor trailers.