Hi All, This is literally my first post, but have been a lurker for many years! I recently had an opportunity that netted me a free mac pro 5,1 (Mid-2010) and decided to upgrade the !@#$ out of it. I upgraded the CPUs to the 5960s, upgraded the RAM to 32gb, installed USB 3.0 card and (2) PCIe SSDs. Then my last hurdle was the GPU; and I have fallen and can't get up. I am hoping someone out there has either had my same issue or knows what i may be doing wrong. I first bought a GTX 980ti off ebay, just a stock PC version. I did my research and this showed to be the card for me. I do work in 3D modeling apps like Maya/Zbrush, and I was planning on dual booting into windows so i could game. So i order the mini 6pin to 8pin cable, download latest drivers from MVC, install both drivers and latest CUDA, while the original Radeon is in the machine. I also set up screen sharing with my mbp just in case, because i notice that the Nvidia web drivers keeps defaulting to OSX default driver. Despite changing it in preferences/locking it. There is seemingly enough power as the lights come on and the fans spin. I know that no boot screen will show, but after 10 mins of looking at a blank/black monitor screen i decide its not working. So i attempt to screen share in from my laptop, and it just hangs on "connecting". After another 10 mins I assume its a no go. Do some web research and see that the GPUs like this especially the 980ti edition, may need more power. So i order more cables: 2x Mini6 to 8pin, and Sata to 6pin. Just to see if its because the GTX card isn't getting enough power. Still same result. So i think maybe the card is bad and i am about to contact the seller and cry, but before i do that, let me put it in a Win 10 PC i have. 980ti loads up no issue. Looks/works great! I had a MSI GTX 970 in the PC, and figure well this must be a lower rated card let me try this in my cMP instead. Using both the low power/extra power set up, i get the same blank/black screen. So if you have stayed thru my story this long, Thank you! If you see anywhere I might have gone wrong or have any suggestions on what to do next, besides send it to MacVidCards or contact them, cause my piggy bank is empty and can live without a boot screen. I am using the latest version of macOS Sierra and downloaded the latest nvidia/cuda drivers from MVC: 10.12.4 (16E195) 318.104.22.168f01 Should I try installing El Capitan? Should I trade the GTX 970 for an ATI RX 480? Any words of wisdom, support, troubleshooting ideas, etc. would be more than appreciated! Thanks for reading!!