It started with my mid-2012 rMBP powering down whenever it switched to the 650M and sometimes randomly causing kernel panics. From grey screen that has centered messages about your computer about to shut down, etc. To bootups that wouldn't boot unless I held down power for a longer time. Then I tried resetting everything I could find, SMC, etc. Shill shut off. I uninstalled gfxCardStatus to see if it would resolve the issue, nope. Tried settings to disable automatic switching, nope. Ran into this discussion on Apple's website: https://discussions.apple.com/thread/5300005 Lots of GPU panics, same message readouts on our 10,1 Macbooks. I still kept searching though and it finally made sense. My fans would wind up having iTunes open or some other menial task. I read somewhere else about maybe the computer wasn't getting the right temperature from the GPU in order to cool it - apparently the GPU is shut down when it reaches a critical temperature. Ordered the Pentalobe screwdrivers and opened it up today. Ran numerous games and rendering programs on the dPU, fans aren't even screaming. Before today it would have caused a kernel panic in less than a minute - the screen would flash and turn off.