So, hopefully the above info will help most people. It didn't help me. The only thing that worked was this last-ditch effort before getting a heat guy, or baking the logic board in the oven. It takes like 10 seconds, and I think it's worth a try, if you're in the same situation as I was. But try all the above steps first, as they're non-invasive! My suggestion is a little violent & risky. I felt like I had nothing to lose, so I pressed stupidly hard on the GPU, as detailed in this link. It sounds barbaric, but it actually worked. And it was a lot easier than a putting the motherboard in the oven. http://perfectfitcomputers.ca/macbook-pro-retina-gpu-fix-a-faster-no-bake-approach/ This won't be for everyone. But if it helps even *one* person... awesome.