Gtx 660 overclock

help i have an asus gtx660 dcu2 (top edition) and want to overclock i have 1 problem is soon as i raise the core clock to 1 mhz it becomes unstable (the power target is already on 110% (the max for a 660))

i think since this is the top card that asus already pushed it to its limits but i am not sure temperature is no problem it stays below 60 c   all the time

does someone knows if this is normal

 

btw my core clock is 1157MHz

Use msi afterburner to give it more voltage. If you've already maxed out the voltage just leave it.