#1. Check your auto parking brake settings. If your parking brake sets automatically and you attempt to drive you will get a jerk till it releases.
That is normal for the auto system.
I did not like that so I turned it off.
#2. Are you sure that is not the ABS at work. How were the roads? You had December for your limited. Any Ice, snow, or water on the road can activate the ABS under certain braking/speed conditions.
I would also recommend taking it in if you have any concerns about the braking abilities of the vehicle.