DPS difference in reg from herioc?Follow

I am a hunter in almost all epics, and my normal dps in a herioc is 2200 to 2400. but I went to help guildys in a reg instance and my dps dropped to 1300?

Is this because it was a reg instance? my dps on the boss's was still around 2000.

Is it something I was doing wrong or does dps just normally lower for regular instance?

Thank you for any input on the subject
Casper