Ok. Than you never added gpu powermanagement for your Mac Type ID (MacMini3.1). Same for me iMac5,1 , i use, hasnt any AGPM active.
MacMini didnt have in real such an gpu so, AGPM is not active
Thats OK for Apple Machines.
To getting AGPM working , better visit other thread, too offtpic that driver thread.
In short: You need 2 injectors (like AHCIPort) which are prepared for your gpu dev-id and Mac Type ID and put them into the /Extra/Extensions + .mkext.
One config is much more easy , only one key (iMac5,1) > yours, And one gpu deviceID(0191) > yours.
The other . plist is much bigger and has lots of iMac5,1 entries to change to yours ! Dont miss one to edit, otherwise no effect.
Attached both , change my used iMac5,1 into yours (all occurences !) and gpu deviceid 0191 (only once) into yours