Hi all, We have a 27" iMac that is having some severe graphic issues. I've attached some photos to explain the problem. We mainly use this machine to edit in Adobe Premiere CC and for use with other Adobe products. Our issue is that periodically (maybe ~8 times a day) the machine will either: a) start showing distorted graphics b) freeze completely and require a hard boot. I brought it to the Apple store and they ran hardware tests and no problems were found. I also have reinstalled the OS. Even right now as I'm typing this there's some blocks of white that are stuck on the screen. (Image attached) Any thoughts on this? Specs shown below as well.