24.7 MH/s with your config and 1100 2000 OC 
I have 2 Gigabyte (micron) cards on the same PC and they do about 30MH/s with the same config. weird 
I'm not surprised, few motherboards performs very worse when mining on them and the only way to get out of this is trying a new OS, LINux OS, HiveOS, Minerstat OS, simplemining OS, make your choice and see if the problem is solved or not, I used to have 5 different motherboards for mining and I've experienced such before I have 2 Gigabyte (micron) cards on the same PC and they do about 30MH/s with the same config. weird