You actually have it running at 150% power limit. That is too much and probably a good way to overload your GPU. Most people run their GPUs at the low value of 65%.

With regards to coreclock, you also have it set to the MAX value. Bad. Thats probably why your miner crashes resulting in the decrease in hashrate. Your mem clock seems to be the only sane value on your config and you could probably increase it slowly. Make sure to do your research before overclocking else you might end up destroying your hardware.