I Oc'ed my GTX 580 matrix to 940 Mhz with a voltage of 1,138 ( I wan't it on 1,130 but it automatically goes to 1,138) and it is STABLE with good temperatures around 75c but here comes the problem: My problem is that when I start my PC it is on 1,150 and yes I did click on burn but it keeps going to 1,150 and when I change the voltage to 1,138 it suddenly says 0,343 but in GPU-z it says 1,138. and on the monitor it says 1,488.
I've ASUS GPU Tweak 2.3.9.2
Here is a screenshot:

I also had another thread on this forum with kinda the same problem: http://rog.asus.com/forum/showthread.php?32942-Lowering-Voltage-doesn-t-work&p=264076#post264076
I hope somebody can help me