2012 Expedition EL, 5.4L, 4x4, less than 40K miles (original tires). It's my daughter's vehicle and she uses it to haul my 4 grandchildren, all under 5 years old (2 sets of twins). The last long trip she and my SIL took they experienced a "violent" buck/jerk upon backing out of the throttle at about 70 mph. This only happened twice during the entire trip, but it was violent and LOUD ! It definitely came for the transmission/driveline. The vehicle has been back to the dealer and they have found nothing. I can not seem to find anything with Google searches. Anyone experience anything like this ? Any suggestions on what to checks ?