Fresh suspension on the truck ?
Ball joints, tierod ends, etc, as new ?
Tire choice and inflation.
Trailer tire choice and inflation.
Trailer chassis all correct.
Experiment with different WD settings.
Yeah, it's all new. The tires probably could be upgraded to a LT, and I might go with a smaller diameter to get a stiffer sidewall (it's geared quite high so it wouldn't hurt). They are at max pressure for the tire, 44 psi.
I had an old Passat that I wanted to gear up so I got the next size taller tire that would fit in the wheel well. That worked well so I went another increment up on my next set of tires. That made for a less controlled ride than before. I think you can go too far in the tall tire direction. The tires on this truck are pretty tall.
I guess the trailer chassis is correct. It's new too. The tires are nothing special, some H118 brand or something like that. Might not hurt to go with a better set there too (it's tandem axle). Max pressure is 50 and I currently have them at 45. I know, everybody says go to max; just haven't gotten around to it.
I could crank on the WD bars a little more too. The front doesn't move but it could go down a bit as the rear goes down quite a bit.