T680 vibration

Got a 2020 t680 with x15 and endurant 12 sp auto. Recently i have developed a low speed vibration. When i say low speed i mean its not fast like a u joint would be at this speed. It doesnt start until i get above 70 mph. It doesnt do it all the time. It will start and go a mile or so and go away. Of course it comes back. I cant make it do it but if i let off accelerator if does get better but will come back. Put new michelin tires on and Have balanced all tires.i have put the old tires back on and reinstalled the new ones. No difference. centramatics on all axels. I took them off and now have back on, no difference. I have put new rotors on front and drums on back along with brake pads. New carrier bearing. Had king pins and bearings verified on all 3 axels. New bushing in rears and 3 axel alignment. Nothing i have tried has made even the slightest difference.
Has anyone else had a similar situation? Do you mind sharing your solution?
Thanks