I've found that with too little tongue weight, things get dangerous QUICK!
We've got a Vermeer trencher/front bucket that has almost killed a few of our sparkys because they didn't load it far enough forward on the trailer. All of our trucks are 3/4 ton and have rear swaybars. That's why I didn't chime in sooner.
I've found that with the death sway, neutral and using only the trailer brakes gets everything back into control so that we can pull over and adjust the load.
Funny story, I scared the shit out of one of our new apprentices when we had a trailer start fishtailing on a curve. He practically worshipped me afterward because I seemed so calm and in control when, in all actuality, I was screaming, "OH SHIT, OH SHIT, OH SHIT!" in my head.
Bravada G80 3.73 converted to selectable 4wd.