Stuck at Hell Act 3 Boss

Hey guys, I'm having problems passing act 3 in Hell. I have all yellow gear tier 13+ with STR and VIT on most. I am level 73 with 19,600 health, 191,000 attack and 1.28 million defence. My main problem is my attack. It says I am only 28% of what I should be. How am I supposed to get more attack other than waiting for an epic or unique sword?