You shouldn't use Idol of Mutilation; use Idol of the Corrupter instead.
You have horrible professions.
Some easily obtainable gear upgrades:
Bracers of Swift Death (crusader orb LW recipe)
Knightbane Carapace (crusader orb LW recipe)
The neck from conqueror badges
Footpads of Silence (runed orb leatherworking recipe)
Death-warmed belt (runed orb LW recipe)
legs from conqueror badges
Slightly harder things:
Clutch of Fortification (triumph badges)
Duskstalker shoulders (triumph badges)
Glyph of Mangle is horrible. This should never be taken as a bear. If you're having problems with Growl missing, take the glyph of growl.
Expertise is your #1 threat stat - twice as good as anything else. Consider getting expertise on gloves as an enchant.
Finally, my suspicion is that you're not mauling enough and not berserking often enough. All of your threat abilities - mangle, lacerate, swipe, faerie fire - and anything else you might use like demo roar and berserk - should be macroed, and they should look like
All of them. If you don't want to do that, fine - but every single time you do an autoattack you should maul. Every time. Without question.