This is on your shamans?

Here is what i do.

5 Shamans:

Standing the door killing the 4 adds that come out to take down the shield. Toss 5x Gift of the Naaru on the "main character"

/tar Party1
/cast Gift of the Naaru

Make sure you are using Frost resits totems and 5x healing streams. Chain heal when needed.

I find that once you get this down, the boss becomes really easy. The instance it's self is really fun IMO. I use it for farming Enchanting mats.

Edit: I actually just ran the place then ran Gundrak ( Normal ) With the changes to shamans, I killed Trollgore is 18 seconds >.>

Edit...again.... : If you stand in the door, kinda LOS the boss and let the 4 adds come to you, you don't get any adds that would come down the stairs @ you.