Please get out of that habit. You should only use Power Slash to establish aggro and Souleater otherwise, especially as the off tank. By constantly spamming Power Slash, you will likely take the boss at an inopportune time and surprise the healer since they aren't going to be expecting the tanks to suddenly be fighting for aggro. Assuming a comparable ilvl, your opener as MT should be...
Optimized - (Better suited when you're comfortable on tank/with a reliable group)
High Threat - (Better for 24 mans and pugs)
You should also get into the habit of Provoke + Shirk, which helps the MT maintain aggro without the need of more combos or tank stance.