You need to get all the glyphs, first of all. That's absolutely huge. Second, if you're already 5 points into arms already, you may as well spend the 3 more to get Deep Wounds. It's far better for threat than Cruelty, and certainly better than the 2 points you have in Blood Craze.
Likely, though, it has more to do with what you're doing in terms of rotation and setup. Are you marking targets before pulls and concentrating on Skull? How are you prioritizing ability usage? When are you losing threat, and to what sorts of behaviors?
Finally, this thread belongs in the HALP forums, not the Theory and Mechanics forums.
Kathy, I said, "I'm lost" though I knew she was sleeping
I'm empty and aching and I don't know why
Counting the cars on the New Jersey Turnpike
They've all gone to look for America