Op, I've got over 300k in rams since 2011. I currently own three and have a 4th on order.
I've changed rear control arms on all except 1 by 80k. The one I didn't change had the vibration and someone wanted it more than me, when it was sold. Who knows what the new one when delivered will hold.
From my experience, rear control arms, bilstein 5100s and good tires, Michelin, Cooper or other name brand tend to address the majority of the issue. If you still have a vibration then you need to go into rear brakes, rotors and pads, maybe even shoes for rear brakes.
If you have a vibration after that, depending on cab size, regular, quad or crew, next suspect is. Depending on Trans and driveshaft, center bearing and u joints.
If you have checked or changed those, then you need a very focused driveline consultation.
My issues have been fixed by addressing control arms and shocks. Never needed to go further as it fixed the problem.
Tires normal replacement cycle, I run cooper's and brakes normal cycle, I run power stops z36.
I have a supercharged RCSB lowered 6 in the rear, that has seen multiple high speed runs well into triple digits , 2 crews that i drive and tow with coast to coast. None of them have a vibration.
I hope my experience helps you identify your issue.