Video Card Issues Galore

[MTTDVS]

I'm having some serious issues with my Mac Pro 12 Core 3.46 running El Capitan, and 12HD.

After a couple of years, my video output starting acting weird. I have 3 screens:
2 Mini-Display to DVI (control screens) - 1080p using the Accel active adapters.
1 DVI to HDMI (1080p video ref LED TV)

After an hour or so of use, one screen will go out, triggering the other 2 to refresh. Then they all come back on and continue to cycling randomly. This seems to have gotten worse...It would take the system most of the day, about 2 weeks ago, to get to this point...now it only takes about an hour of running PT to affect it.

I confirmed the monitors themselves work fine, so I just upgraded the card itself (the stock 5770) to a Sapphire HD7950 Mac Edition from OWC. Was fine for a hour or so, until I booted up protools and started getting into the edit...then problems again.

What gives? What is the solution to this problem, and why, after working fine for months does it start going downhill? I've been on El Cap and 12.8.1 Since fall 2017.

THANK YOU