Since your shamans are 75 make sure your usuing lava burst after a flame shock. i have a castsequenece macro for it. it does an insane amount of damage, almost killed the first boss before his skeletons could rez. But as for the last boss after you kill him in phase one drop mana totems if you need and heal up and run behind a pillar. on all my attempts he does that aoe right off the bat and knocks me down to half hp. then drop fire elementals and bloodlust. then on you tank just run through him when he does that slam or smash. just make sure you flame shock lava burt when its up. i know mine are hitting for 4700ish.

http://www.wowhead.com/?item=38361 this item may help also. you get it from doing the dailies.

good luck