I'll add that Rancho 9000XL on front and rear of my Diesel Excursion with F350 springs are a very good combination.
I have adjusted the settings a few times and recall a setting that made it feel a bit "orbital" in sway. Changing the setting fixed it.
I *think* it was the front to back interaction, not the setting itself in my case. Once I got them both where I wanted, it's been rock solid for some time.
Not saying you did anything wrong, or even that the shocks are "right" for your rig. You know your experience better than we do ;)
I would recommend using adjustable on all 4 corners if you were going to change shocks again, regardless of brand. There are just too many variables and interactions IMHO. There are people out there who can get non-adjustable shocks "just right" the first time, but I'm not one of them, I needed the adjustable ones ;)
Good luck with Rancho. I had to fight for the rebate for a few months, though I think that was more their gift card provider than Rancho.
(I do recall getting 2 different defective shocks with damage, including to the adjustment knob)
Hope you find a good combination for your rig!