2- Add the device id of your GPU to the appropriate kexts.
Add your device-id to the cedar section of the AMDRadeonX3000.kext and anywhere in the AMD5000Controller.kext
- Go to /System/Library/Extensions/
- Copy AMDRadeonX3000.kext and AMD5000Controller.kext to your desktop
- Right click on the AMD5000Controller.kext and click show contents.
- Open the info.plist (using TextEdit or any plist editor)
- Find the IOPCIMatch key and you'll see many device-ids
- Change any of those device-ids with yours (eg. 68981002 -> 68F91002)
- Save (make sure you don't change file extension)
- Right click on the AMDRadeonX3000.kext and click show contents.
- Open info.plist
- Find the AMDCedarGraphicsAccelerator
- Under IOPCIMatch, change 68E01002 to 68F91002