Heh, definitely not a tank issue (edit: or any other toon, now that I looked at them all). Yours blows mine away from when I first beat it.

In case you glossed over it, but shadow resist aura on tank (for shadow bolts) and frost resist totem from one of the shamans. Use mage armor on the mage (more resist). Keep in mind that you can resist being ice tombed altogether, so high resists makes this fight far easier (and easier for the achievement).

Should be obvious enough, but target and blow down any tomb that does land right away. You can bubble and iceblock out of tombs, too.

Keep all your slaves RIGHT behind the tank, do not spread out. Consecration will not only ensure the skeletons stay on the tank, but will also help damage the tombs.

The major damage in this fight is really the tombs, so your focus is really just watching for those. Once you work out how to manage the tombs, the fight isn't too bad.