Taken all the steps to prevent sway. Still swaying. Help!

Try setting the cruise control on the truck next time you tow. Slow down just a tad. I find it makes for a much more relaxed towing experience when I don't have to be constantly monitoring road speed, and just concentrate on steering and the mirrors.
With a high sided trailer it takes awhile before you get used to what is just a twitch and what you need to react to. In other words stop fighting the trailer.