Ask the question in this section. Probably it is a frequently asked question.
I kinda doubt that, but here goes (5th post, woohoo!):
Why am I seeing reduced performance from my 5-GPU miner when connecting to Slush's pool? I get a constant 1650MH/s reported by Diablo when I'm on DeepBit (although DeepBit reports slightly less) but anywhere from 700-1300 on Slush, with a current 10-round hashrate of only 1161 (that confirmed by submitted shares as well as Diablo reported hashrate). LOTS of fluctuation in hashing speed, peaking well below what I know the miner can do (and no, it's not stales, which are currently ~0.3%). If anyone but Slush can help out I'm all ears