I had a 2015 Tahoe that was doing this exact same thing, it was so bad the dealership bought it back. I then purchased a 2016 Tahoe that is having the rough idle issue!! GM said replace the motor mounts, I'm 1,100 miles out of warranty so I have to pay out of my pocket for the motor mounts. Is this a sure fix? The dealership says probably not. I have been going back and forth with GM about this and they refuse to be of any assistance to me. Possible Lemon Law case here, maybe even class action lawsuit. GM is aware of this issue and can't get their acts together to fix the problem.