WTF is up with my DPS!?

Alright so I have been having major issues lately with my DPS in ICC and other raids. I don't know what it is. I went to ICC on Sunday night, we got up to professor putricide or whatever his name is. So anyway I am hitting hard, criting big, pretty sure I was pulling tons of DPS. Well I thought wrong once again. I went to go check my DPS and i cannot do more than 3.8k DPS. That is bad in ICC. I was in last with DPS and the guy above me was at 5.5k. My gear score is 5300, and I SHOULD be able to pull a lot more than a miserable 3.8k right? Well I don't know, I need to figure out this problem before no-one wants to pug me anymore because of my low DPS. Really driving me nuts!!