GTX 980 hammering sfx power supply? Why did it start after months of working flawlessly?

[RealBeard]

So, something I'm not quite sure how or why it happened. I made a compact build in May. Worked flawlessly through summer, I walk away for two weeks in November and since then the computer resets whenever I start up a gpu intensive game or app. Browsing, netflix, zbrush, photoshop, they all work fine (cpu intensive). If I run even a basic benchmark, the computer reboots.
Thinking it was the silverstone SX600 PSU. I swapped it out for a corsair SF600. I worked for 3 days before the issue started up again. Doesn't seem to be a GPU temp issue. and the case never goes above 60 degrees. I'm hoping someone has encountered this issue as well or at least can tell me if it's a new GPU I need. Please! Thanks!

Other things I have tried:
-Full display driver clean and update
-UEFI update and CMOS clear
-Monitor ambient temps for spiking (reset happens at 42 degrees C)
-Swap power modular connector cables
-Direct X and .Net re-install
-Mem test
-Drive integrity check

Intel Core i7-5930K @ 3.5GHZ
Asrock X99E-ITX/ac motherboard
G.SKILL Ripjaws V Series 32GB (2 x 16GB) 288-Pin DDR4 2400
EVGA Reference Geforce GTX 980 (Driver 376.33)
Crucial BX100 500GB 2.5" SSD
Seagate Barracuda 7200rpm 1TB
Crucial SF600 SFX 600watt PSU
SilverStone RAVEN Series RVZ01B Case

Windows 10 Pro

 

[hang-the-9]

Really the best way to see if it's the video card is to test it in a another system with a good power supply. If it ends up doing the same thing, card is going bad.