WHILE PARKED IN MY DRIVEWAY. THE AUTOMATIC LIFTGATE GOES UP AND THEN FALLS HALFWAY, GOES UP AN THEN FALLS BACK ALL THE WAY DOWN. IT HIT ME AN KNOCKED ME OWN THE FIRST TIME. IT STARTED IN JULY OF THIS YEAR AND DOES IT CONSISTENTLY. I COULD HAVE BEEN SERIOUSLY HURT OR A CHILD COULD EVEN BE CRUSHED AS IT IS EXTREMELY HEAVY. I CANNOT USE THE REAR COMPARTMENT AS THE LIFTGATE WILL NOT STAY OPEN. THERE IS A LAWSUIT ON CERTAIN YEARS FOR THIS VERY PROBLEM AND GMC HAS A TSB UP THROUGH 2014 BUT FOR SOME REASON THE 2015 MODEL IS NOT INCLUDE EVEN THOUGH IT HAS THE EXACT SAME ISSUE. HERE IS A VIDEO OF THE ISSUE. THIS IS ANOTHER TERRAIN AS I DON'T KNOW HOW TO GET A VIDEO OF MINE ON YOUTUBE. HTTPS://WWW.YOUTUBE.COM/WATCH?V=U3NCKL-DETA