I don't know if you know this, but....A Dead DPS is not a DPS!
Are you DPS utilizing their CD's correctly? Fade, Iceblock, Tricks of The Trade, feint, Feint Death, Divine Shield? Whatever it takes for them to drop agro, they need to do, because...
A DEAD DPS IS NOT A DPS!!!
Let me tell you man, Naxx is a huge Noob Checker Play Ground, i don't know how well Warmane has debugged and toned Naxx here, but i cleared it every week in 3.0 Retail in 2008 and it was my first raid experience ever, I just got lucky and got to raid with some friends a worked with and their friends happen to be really nice and really explain the fights. :D My personal experience from Naxx is that it's a Noob Checker. Like how Patchwerk is a DPS checker, Razuvious is a controller checker. Basically how well can your teammates control what they they're doing. DPS when it's really safe to DPS, CD when it's time to CD, and use proper rotation when mind controlling the trainie NPC's. Other fights are even harder like Helgan's Safety Dance.