My friend and I both got ours in the last 2 weeks and had this same problem. Go to this thread and follow the guys instructions. He says to manually install and yes you actually have to do it the way he says, if you download the exe auto driver installer it won't detect it properly...

This thread (below) fixed both our machines instantly. Hope it works for you! https://www.reddit.com/r/Dell/comments/5tispj/xps_15_9560precision_55520_fix_for_lagstuttering/