They only time I get that is when I'm towing my 5th wheel or have a heavy load in the back... There is a reason for it under those circumstances in that it's the angle of the driveshaft... Even then I have to be leaving a stop pretty quickly for it to do it and it never does it other then from a full stop..
Unloaded I've never had it shutter/vibrate... Definetly needs to be seen by a different dealer...
Ken....