You can also cast a heal over time on the pally (via cleric) before you pull so that the cleric doesn't have to draw aggro immediately after a pull, giving the pally some time to establish aggro. Also wait a couple seconds before attacking on ranger for the same reason. Hard to manage heals when you are boxing if the aggro keeps switching focus.
Dread Gaze is a very fast casting AOE taunt that generates 250k hate. No need to worry about the healer or ranger pulling aggro once you've cast that.