Tom,
Your WD hitch is not set up correctly. See
this thread for detailed instructions on how to get it done.
I think you would benefit from a new hitch if your old one has a fixed hitch head on the shank. That type of hitch is fine IF it is set up and welded in place for a particular truck/trailer combination but it most likely is not constructed right for yours. A new hitch will run you about $500 or a bit more, but for that money you can get a quality WD hitch with built in sway control like the
Reese Strait-Line hitch.
Reese Strait-Line hitch.The Equal-i-zer hitch
Equal-i-zer hitchor the Blue Ox SwayPro.
Blue Ox Sway Pro hitchAir bags or other types of rear end propping up is not the way to go to solve your problem. A WD hitch is designed to do just that and should be the fix needed for you.
Barney