Doug,
As BarneyS stated (and it often is overlooked) The weight carrying capacity of the hitch is normally less than the tongue weight of a TT. The WD system allows this capacity to increase as it changes how the load is applied to the hitch itself. Basically it lifts up on the rear of the receiver and presses down on the front therefore reducing the leavage on the hitch and allowing it to carry more weight. That said, if your complete hitch including the ball coupler is rated above the loaded tongue weight of your TT and your TV sits level and steers fine there is no need for WD. This must be checked very carefully first. But why settle for this since you have WD and if hitch height and TT loading is right the WD will make everything better.
In your case I suspect the following:
Your hitch height is too high causing your TT to sit level or "front high" without the WD. (Did you leave your ball coupler set at the same height as it was with your previous TV and now it is alot higher with your new TV?) This would explain why you have sway with the WD and not without as the WD make a TT that is " front high" even more so thus sway would be more likely.
If my assumtions are correct, I suggest you lower your hitch height until the TT is "front low" and then use the WD tension just enough to bring everything level. (The WD will only increase the strength of your hitch and you have it so why not use it)
I say all this because I had the same situation once. I pulled someone elses TT and the hitch was set to the heigth for their TV. Mine TV has much higher or the TT would sit also level without WD but sit "front high" without. The TT would sway some with the WD and not at all without all becasue the hitch heigth was too high to begin with.
