Can you check this GPU ASIC percentage with GPU-Z ? Weak silicon can be the source of this low hashrate. One of my 570s is unable to reach 30MH/s, the 2 others can sometimes reach 31.5MH/s (average 31MH/s).
ASIC Quality: 70.1 %
My worst is 70,5% and is far from the 2 other GPUs wether it's ETC/ETH, Neoscrypt or CN cryptos (100H/s worse in CN V7). You may not be able to extract much more speed from it.