Have you actually weighed the trailer and tongue when loaded? If not, that's your first step. Hitch weight should be 10-14% of the total trailer weight, but if it isn't it could be causing problems.
If hitch weight is ok, next thing I would do (personally) is replace the E2 with a regular Equal-i-zer. I believe this adds 2 more friction points in the hitch head. And I'd probably ditch those P tires, too, in favor of some with stiffer sidewalls. That should do the trick. Not sure you should need air bags, although they couldn't hurt.