I cannot get this to work on Mac Pro5,1

I’ve used OCLP on numerous devices with no issues, but for the love of god I cannot get this to work with a Mac Pro5,1. It’s actually a Mac Pro4,1 that’s been flashed to a 5,1.

I’ve ensured the firmware is 144.0.0.0.0.

I have Mojave installed with an RX580 - no issues.

I build the OCLP install on the external USB with the RX580 installed during the build process. Then swap it out for the GT120 so I can boot into it with the built in bootloader.

Works fine, I’m able to get it installed. Then I run into some prohibited sign boots. So I go back into the Mojave partition and reinstall the patcher on the new Monterey disk.

Then it boots fine, but there’s no hardware acceleration. The system recognizes the RX580 in System Details, but it’s slow as shit. And if I try to run a compute test in Geekbench, it says there is no supported compute device installed. So something is wrong with the AMD drivers.

Ive wiped and reinstalled 3 times now, googled troubleshooting to no avail, and im getting frustrated. Desperate for help.