many things factor into that your ilvl doesn't necessarily mean you will have high DPS if you spec into the incorrect stats it won't matter how much ilvl you have so one thing I suggest to do is too evaluate the stats that you have on your gear second I would suggest to manage your own cooldowns I'm not sure if you are doing that already but I always suggest to manage some of your big burst cooldowns also what fight are you talking about?
i use my own couldown and my stats was critical and mastery