If the picture of the trailer you posted a few posts above is your trailer attached to your truck, it looks like the trailer is a little nose high. That, in itself, can cause sway. I think someone already suggested it, but before you do anything drastic, get the WD hitch manual and set up the hitch yourself. See if that helps your problem. You have enough tongue weight with that trailer. My only other concern would be (and I already mentioned it) is that the WD hitch they sold you is probably too light for that trailer. The tanks and storage area are in front of the axle. That model is, by nature, tongue heavy.
