little advise for opening threat in heroics
Try to get 2 stacks near end of a trash pull.
Then after you charge into next group - thunderclap again (giving you 30% boost) and your shockwave with a cleave should make things stick to you. As you get down to the last mob or 2 start stacking up your thunderstuck charges again by using thunderclap. If you don't get 2 charges before that last mob dies then TC after dead, roar (rage builder), charge and thunderclap again. Worked great in instances like DTK, Gun, Nexus, UK & UP where you can zip from one pack of mobs to next. Worked horribly in Violet Hold and Occulus where rage deterioted too fast between packs. Using shockwave resets your Thunderstuck counter to 0.
My last few heroics I think the DPS were a bit confused with me TC'ing inbetween pulls but using this helped me a lot on initial threat. Also, it kind of sped things up a bit and the Shadow Priest was bitching about being OOM. I guess with no mana, a little less threat to worry about.