It's Definitely harder to get a decent threat lead in Cata,
especially if the DPS doesn't look at, or cares about, aggro/threat.
your rotation sounds fine for AoE groups, but most mobs in dungeons aren't meant to be AoE'd down anymore,
I would try to at least mark a skull, and use some devastates, shield slams on it, to make sure it sticks to you, the rend/TC/SW should take care of any healing aggro & splash/aoe aggro.
gear would definitely make a difference though, you still have lots of level 80 gear on you, replacing this with questing greens/blues should make tanking a bit easier. (more stamina, mastery, avoidance, strength...)
also, if rage isn't an issue for you, you could take the points out of 'battle trance' and spend them elsewhere, ('war academy' or 'blitz' come to mind)
The smart (shaman) player will actually make reasoned judgements about his gear, talents, and spells, instead of just blindly fumbling around in the dark hitting every button Blizzard has given him to press.