To the OP...with that setup your main tank was probably slacking big time or there was a major bug going on. My guild never runs a coercer + dirge in mt group and we only got 1 troub atm so at least 1 or 2 of our wizards normally go without deagro but we don't have any agro problems so dunno how much I can help you there.
A bit off topic tho, after you figure out the agro issue you might wanna go for a bit different spell order. I'd say for sure get ball of lava in the rotation sooner. Its our bread and butter and its not nearly as dangerous as nova or fusion. Also use sunstrike less. In a raid situation where dots will have full effect even Fiery convulsions is a better spell then sunstrike. It casts faster and the average dmg is about the same if not higher then sunstrike which means more dps. Also don't use cease so early. You really don't need to use a deagro before you cast any decent size nukes. I'd say something like...ball of lava -->cease --> ice nova --> concussive --> fiery convulsions (to get that concussive off real quick without more agro. I like a combo like that midway thro fights and i think it works especially well about 15-20 seconds into a mob.
Anyhoo thats just my 2c.