I've also noticed that if I put in an argument that cudaminer doesn't like, I have to reboot my computer since it drops my GPU clock speed to 750mhz and seems to lock it there.
Try enabling and disabling SLI in such cases. Not sure if it will help with newer nVidia cards, but works just fine for locked-after-error 480s ever since I found sometimes I manage to lock them at lower speed.