Driveshaft problems of the 2020 Hyundai Palisade

Vibration at speeds of 64/65mph and up. Not sure if driveshaft or transmission. Hyundai has issued a TSB but will not honor it. I have asked 2x for dealer service dept. To evaluate this problem. They said they do not have to honor this TSB. I have seen on forums others are having same problem with cars made in December 2019. It is painful to drive on the highway and I do not know if it is the driveshaft, will it break? will the transmission fail? this is a brand new car purchased new and it is unsafe to drive on the highway and I cannot get Hyundai to look at the problem and they have sent emails saying tough luck. This is anytime you are driving on interstates or highways with speed limits of 70mph. . At around 64/65 car steering wheel, seat, floor vibrates unless you go below 63mph. Happens every time. First time was driving home from dealer on highway--been reaching out to Hyundai USA since July been to dealer in July, August. . . But always told appointment will be two weeks to 6 weeks away.

Purchased vehicle and when we drove it at highway speeds (64-75) there was a severe vibration with low frequency rumbling (sounded as though driving on rumble strip). If we drove above 75 the vibration would lessen. We brought in into the dealer and on the first visit they first balanced tires, no change noticed although they gave us the vehicle back. Second visit they replaced rear tires and force balanced all tires, no change. Then they replaced front tires and replaced the rear drive shaft after having told us two weeks prior that they had measured the first one and it was within Hyundai specs. The replacing of the drive shaft improved the low frequency vibration but did not completely eliminate it. We are currently waiting to hear back from Hyundai corporate for a buy back.