I have a 2014 LaCrosse AWD. So on a normal take off everything is fine. If you takeoff quickly, it will shake or vibrate. If your running along and give it gas and it downshifts it will shake.
We held the brake pedal and gave it gas, it doesn't seem to be a motor mount. It idles fine and is fine with a normal takeoff. Not sure WTH is going on.