I wonder if this issue has anything to do with the fusion drives... Also, another thought... Let's compare for a second a car. When pressing the gas pedal all the way in, all newer vehicles have a "governor"; it's job is to regulate the acceleration and stop it from going over higher RPMs just so that you won't blow a gasket or shoot-out a piston. My issue is the same as you folks, when pushing my (loaded, late 27 iMac, 3.4 i7, 1tb fusion drive) it shuts off... Usually while scrubbing and multitasking. Is there a way to limit data process to stop update/refresh when reaching certain level of CPU processing? With iStat, I've monitor temperature and accelerated fan speed. Genius Bar scratches their head. Honestly don't think changing the graphics card will fix it; I've encountered the same issue with a newer iMac with the 4gig video card as well... And based on reading this forum it seems to me this is issue not only affects iMacs, also MBP, and I wonder if the new macpro trash cans have it as well... And wouldn't be surprised. Could it be possible that, Apple, in the spirit of unleashing power off all those horses could have left the cap off and video editors and graphic artists at pushing their machines have found a way to get to their machines breaking point? In that case, it all suggests OS issues... But how far back can we go? Before Mavericks? Honestly, tired of this... My 2 cents/rant.
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