I'm having a similar issue, but only in certain conditions.
'21 Power wagon with 35x12.50 17's on OEM rims. 45/37 PSI. Now have 24K miles on the truck.
Normal driving with no load, everything is fine.
Did a Baja trip with 100G of gas in the bed and pulling at 6K old military "Bouncing Betty" trailer. Everything was good.
Second trip, similar setup but also had 3 40" race tires in the bed. In the states, I was fine, but on the highways in Baja, I got the sway. A few times it got so bad that it triggered the stability control, shut of power and almost thru me thru the windshield. Speeds varied from 55 to 75. Speed didn't really seem to matter. Sometimes when it would sway bad, I could tap the brakes and it would settle out.
Third tip last weekend, Only had a fuel pressure tank, empty and bunch of camping gear. Not really overloaded. Truck got the sway, but never tripped the stability control.
Had 2 buddies drive the truck and even they could feel it.
It has never happened while driving on roads in the states. Only started happening in Baja on the same roads I always drive, and some new ones. Never had it happen in my Blazer or my F250 down there. Weird part is it didn't happen on the first trip down to Baja with the PW.
So trying to figure out where the problem may be and what a fix is that won't affect driving in the states.
Tires? Shocks? Track bar? Springs?
I do remember CJC I believe said that the track bar bushings would wear out fast and It would be advisable to swap to the Thuren track bar at some point.
Any ideas?