Not sure if I'm having the same issue or not but sounds very similar. 2018 off-road w/KDSS, stock was fine. Lifted with 33s and there is a vibration around the 50-60mph range but it comes and goes. It seems to be there after the vehicle has sat for a bit, and then goes away after I've taken a couple of decent corners at highway speeds that load up the suspension. Leaving my house and onto a hwy to head into town I climb up a hill and it is pretty consistently there when I accelerate to over 50, but then there are two sweeping corners that if I take at close to 60, the vibration will settle down, often to the point of being completely gone.