I would weigh it with three passes over the CAT scale to get all the relevant weights. Load the trailer to get approx 13% tongue weight.
Adjust the WD hitch to achieve close to 50% FALR and see how it handles then. If still experiencing unacceptable ride, I would then adjust up the WD to achieve a "slightly" higher FALR ( maybe increasing it to 60% ), then re-evaluate. At no point in this process of experimenting would I go over 100% FALR.
This is a big trailer in relation to the truck, so it likely is going to take some fine tuning to get it to it's sweet spot.
Good quality shocks on the rear of the truck may help also. I like Bilstein 5100, but I suspect there are others that work well also.