The heroics have been tuned so that you shouldn't be able to manage this with appropriate gear and normal teammates. Sorry.

Grind money somehow or befriend some tanks.
The dual-spec system, whenever it comes out (3.1 at the earliest) should solve your problem, but until then it sucks to be you.
Edit: Do you PuG and keep track of the names of the good members? It can be easy to overlook the work of a good PuG tank because they - well, they make things dull. Their health bar doesn't jump around, they just stand in one place and eat all the damage and the bad guys drop one, two, three, four. Remember those guys.

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Everything in war is very simple. But in war, even the simplest thing is difficult.