Post some pictures here of your rig and your set up.
Maybe some of us who run a dual cam with great success can take a look and help out. Are you sure the 800 lbs bars are correctly matched to the GVWR of your trailer...just cause,"the dealer said," isn't always just so.
Also, some and I say some movement from the bow wave of a big rig is not unusual and should not be considered sway. Are you are the edge of loosing control or just feeling a little "sucking over" when trucks go past?
But, as previously mentioned, the problem might be elsewhere.