check again: u really have to delete any other drivers (kexts) for graphics!
Also, efistudio sometimes cannot change boot.plist because of the permissions, so try to change the permissions of boot.plist every body read/write, generate the string with efistudio, and then copy-past it into boot .plist (use textmate), repair permissions, reboot -have to work...

i know, man, how frustrating can it be - dont give up...