If i where you i would begin with adjusting your build and choise of glyphs, before considering adding HS or Cleave to your rotation, there is alot of threat to be gained from that.
Vigilance glyph alone gives you a 10% lead on TPS over your highest threat DPSer, and a >5% lead on the rest.

Talents like impale, improved revenge, shield mastery and incite should also give you a noticable threat boost.

Starting with challenging shout or taunt wont get you far, as taunts doses not give you threat, only makes you catch up with whoever it is that are leading on threat at the moment. When building AoE threat, its not much else to do then to use shockwave and TC as often as possible, unelss you want to more micromanagment then needed.

Also, make sure to use shield block each time its off cd, as its gives a good boost to Shield Slam threat, wich should be your main source of single target threat.