OK, first of all, core clock and shader clock are linked anyway, so no need to worry about that.
Second, if you raised the core to 1Ghz without raising the voltage, what you say doesn't surprise me. There's NO way you'll get to 1Ghz on stock volts (maybe not even on may volts. My 560 non-ti can't). 1Ghz isn't easy to get to AT ALL. Some cards can do it and a lot of others can't.
Third, I use an older version of Afterburner myself, so I don't even have a Power Limit option, but you can't adjust that on 5xx series cards anyway, so again, no need to worry about that. That's a 6xx series specific thing.
Fourth, I told you how to be able to adjust the voltage, unless they changed it in the newest version. Settings -> and check the "Unlock Voltage Control" and "Unlock Voltage Monitoring" boxes. That's the way it is in Version 2.2.0 anyway.
Fifth, again, don't even worry about changing the memory speed, especially by such a small amount. There is NOTHING to be gained by doing that. NOTHING. Trust me. Just forget about it.
Unlock the voltage control, and start small this time, like I told you to to begin with. You should have known better than to shoot up ALL the way to 1Ghz without adjusting the voltage. That was NEVER gonna happen.