We use HitchVise which stops all movement so there will be no wallowing.
Hitch tightener: no wobble, anti rattle stabilizer device for hitch accessories (http://www.hitchrider.com/nowobble.htm)
There are other similar devices out there, but we like our Hitch Vise, which we have been using for about 8 years.
Hey Barry. I looked at them after seeing your post in the archives. My concern is that given the amount of wallow in in my receiver, that friction that the HitchVise provides would not be sufficient to stop the back and forth movement.