Experiment with different thread counts.  Some people here have reported better results with fewer threads.  My theory was CPU throttling due to high temps.  But earlier in the thread it was mentioned that hyperthreading processors could possibly have a negative effect if the CPU uses hyperthreading for threads that should have a physical core dedicated.  I have 4 physical cores plus hyperthreading, and I actually get the best hash rate with 3 threads, even though I could use up to 8.