I would suggest 2 healers for thorim hard. Or really any hard mode that needs 2 tanks. (cept algalon)

How many stacks does he get up to with your 3 healer set up? We usualy down him at around 8 stacks. By the time he is at 6 stacks we are allready using a cooldown rotation for unbalancing strikes.

Key to thorim hard. Positioning 2 ranged group (max 3 people) to stack and stay away from each other, away from melee, away from blizzard, and away form charged bolt. Easier said then done, but thats the key. (Frost resist aura/gear and any + health buff you can get are good too). And have that ret cleanse!