From the original post, is the trailer causing sway just when there is a significant cross wind or semi going past, or is it doing this all the time?
I agree with some of the above posts, it is probably an issue with not enough tongue weight. A trailer that tows bad will still try to sway a heavier truck, it just isn't as noticable. Either way, it needs to be improved. Let us know what it does after you increase the tongue weight.
Having a sway control setup mask a serious problem is not a good idea. You want that trailer to tow well and the WDH and sway control to make it even better.