2012 rear hatch will not open automatically
Seen where some one else had an issue with that the other day and it turned out to be the battery. When they replaced the battery it went to working normally. Everything else worked fine just not the lift gate. Not sure if that's your issue but might want to look into it.
Hard to believe that yours is a bad battery though with yours only being two years old. Might just be a battery connection issue. Not enough power getting back to the motor. Might want to check out the fuses too.
Search GMC Yukon Questions
GMC Yukon Experts