Need help resolving MacPro 6,1 Black Screen after update

I have an Asus X99 Pro USB 3.1, GTX 1080ti, Samsungs 950 Pro NVME boot drive. I installed High Sierra and everything was working fine, and I ran the supplemental update knowing I could use my USB install to boot without loading Nvidia drivers, so that I could run AGDPfix and install the 10.13 supplement Nvidia drivers.

However, it's not working. I can boot into the installer or into recovery mode, but every time I try to boot into the OS, it gives me the black screen after OS loads, and then reboots.

Does anyone have any ideas how I can boot into something that will let me install Nvidia drivers and AGDPfix? I've tried -x and -s, neither one is working.

submitted by /u/jtfarabee
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