Are you three healing Flintte? What is your healing comp?
We're 3 healing it, me (Disc Priest), a Resto Shaman, and a Monk.
Normally, the Monk comes on his Rogue and our main healer is a Holy Priest, but we've been having trouble getting our tanks to show up, so the Priest usually tanks on his Druid.
The Shaman usually has a cooldown available every time, but the Monk only has Revival and I still haven't gotten the hang of Disc when dealing with heavy AoE damage. I think part of the problem is that Focused Lightning always seems to go out right before Lightning Storm, and it often hits one of the healers, so someone's off kiting the lightning away and then they tend to die because they're not grouped up and healing/being healed.
Our dps isn't bad, I think when we got him to 40%, it was after the 2nd Lightning Storm. But maybe we could try 2 healing it.