Start over with the overclocking.
First overcloc small steps at a time with testing between each step.
Overclock the memory first. Small steps. If you overclock too far you create errors ' which have to be resent. Causing delays not gains.
Next drop the memory back to default speedsand overclock the core.
Small steps with testing.
Once you find the max each runs at reset the clocks about 50mhz slower than max and overclock each a little and test. one at a time. Once you get to the point your score starts going down instead of up,bac off about 10mhz and call it good.
However with the CCC disabled, it will inhibit your Overclocking ability. Go into the CCC, and enable overdrive. Also move the Power control settings all the way to the right. The CCC will throttle your card to stop it from using too much power if you don't adjust the power control settings.
After those settings are unlocked, you can do the rest from Afterburner.
Run GPUZ while you are testing your overclock to verify that your clock speed is actually increasing. But you should start over from stock frequencies.