I wanted to report back that I solved my issue. I'm pretty certain that it's not going to help any of you but here goes...
I am on a Mac Pro 1,1 and was running 3 displays. The Mac Pro comes with only 2 PCIe express power plugs so I was running 1 card in limp mode as 1 of the cards required 2 plugs and the other required 1.
I have since removed one of the cards and determined that was my issue. Just today I was able to route another PCIe express power plug so that I am now back to 3 displays.
My word of advice is that if you are running an upgraded video card, assume that is the culprit.