Recent developments in OpenCore (version 0.9.5+) and the WhateverGreen kext (version 1.6.4+) have patched the dreaded "boot loop" and "VRAM detection" issues that plagued early UHD 770 adopters.
Open your config.plist (using ProperTree or OCAT). Navigate to DeviceProperties -> Add -> PciRoot(0x0)/Pci(0x2,0x0) .