Had the same issue on a demo last week with a 31' machine and like other posters have mentioned this is what we did:

Make sure the wings are level with the center section.  Setup guys must have been in a hurry, ours were out of adjustment leveling them helped alot.

Carry plenty of weight on the guage wheels.....this pretty much cured the wing bounce on the one we were running.

Our ground speeds between 8-9.3 mph.