OS X randomly crashes when 2 GTX 660s are installed

[Ron W]

My configuration:
Motherboard: MSI Z87-GD65
CPU: Intel Core i5 4690
GPU: 2x ASUS GTX 660
RAM: 24GB Corsair Vengeance
OS: Yosemite 10.10.3
Monitors: 3x Achieva Shimian 1440p monitors

I've been having issues with my hackintosh freezing/rebooting ever since I added a second GTX 660. I've got my main monitor connected to the GPU in the first slot, and two other monitors connected to the card in the second slot. I can reproduce the crash by setting the default monitor to be one of the ones connected to the second card, and running GPUTest. I have no problems running it on the first card, but if I run it on the second one it freezes within a few minutes, or if it doesn't freeze the computer lags (even after I close GPU test) until I reboot it. Usually when it happens, the only thing I have open on the monitors connected to the second card is twitter, mail, and iTunes. I assume my screensaver causes it to crash occasionally too, because sometimes I will walk away for a few minutes and come back to find my hackintosh sitting at the login screen.

I initially thought the second graphics card was bad, but I tested both cards (individually and together) with GPUTest in my Mac Pro 5,1 and it never crashed. Also, if I switch the cards around in my hackintosh, the "bad" card works fine and the "good" card has issues. I've tested the cards with both the Nvidia web driver and the stock OS X drivers, and it doesn't seem to make a difference. I've checked the RAM and all 4 sticks are good. I threw an AMD 6450 in the second slot and ran GPUTest on that and it didn't crash (though I couldn't connect both monitors to that because it only has one DVI port, if that makes a difference). I've tried to replicate the crash in Windows as well, but it didn't crash.

Does anybody have any idea what the issue might be, or what I should check next? Any help would be appreciated.

TL;DR: OS X randomly crashes when I have both GTX 660s installed, but both cards work fine individually in both the hackintosh and in my Mac Pro.


This is what was in the console after the most recent crash:
5/24/15 8:02:00.000 PM kernel[0]: NVDA(OpenGL): Channel timeout!