Shimmy shakin' dana 60 front

[Scrub]

I have an 86 k30 with duals. It had a utility box on it which was heavy. I took that off and put a pretty light flat bed on it.
Today I hooked up a trailer that had a pretty heavy drawbar weight.
Net result, the front end is lighter than ever. About five times today, the front end would go into a shimmy spaz attack that made me have to stop the truck.
I drove this home from Phoenix to Oregon and it never did that before.
I jacked it up and the bushing are tight as hell, zero play. I have a little play in the steering box, but I am not sure how to tighten it up as I know you can break a steering box easy if you go too far.
The stabilizer seems to have some air in it or something. It will be tight as heck, then get sloppy and then tight again. I need a recomendation on a new one. My parts guy ordered me a Rancho, but the Ranchos he had (didn't fit) where just about the same as mine, Tight, loose then tight again.

NAPA has a Monroe stabilizer instock.

Which is the best? also, how to tighten that box

Thanks in advance