2019 Mack Anthem with under 4500 miles developed vibration

I bought new Mack Anthem. Now the truck has developed a vibration at 50mph bobtail and about 70mph with trailer. It feels like tire separated but no visible problems on any tire, no mud between rear tires, or anything I can see. Mack said dealer needs to check it out but can’t get in till next week. Was wondering if anyone else had experienced this? What might it be?

 

That’s what I’m doing. Dealer I bought from is seeking to get approval to supply me with another truck until resolved. Meanwhile need to make $$$$

 

Surprise surprise. Mack warranty doesn't cover alignment or balencing. Dealer said it was out of alignment. So went to recommended place and had aligned. Did not resolve problem. (spent close to 1200 on balencing and alignment)
!!!ON A BRAND NEW TRUCK!!!
Back at dealer, very unhappy and they know it! Had it since yesterday morning. They kept saying its not a drive line problem.
Guess what they just called and to "their" surprise it is!!!

Meanwhile....we got first payment coming up. And to this point, the truck has cost us more much than it has profited cause of downtime and shoptime.