1) Don't use the shadow bolt proc immediately. You should be timing it after a tick of drain soul, and also using it to refresh SE which can sometimes be tricky to keep up for a whole execute phase without throwing in an extra hard cast of a shadow bolt.
2) Agony in this case.
3) Again, should be using haunt to refresh SE. If this drops off you've failed and your dps will be below par, so use it on cd PREFERABLY after a tick of DS.