I keep to a priority in this order:
I often forget SW:D because, well, I got into the habit of not using it and it's hard to break. But using SW:D IS the right thing to do, but keep your dots up first, that's the MAJOR damage. Dot uptime is what let's me out-DPS a raid mate who out-gears me. And it's not a minor thing. I even out did him (slightly) in my healer gear (accidentally forgot to switch). The night before I was several steps above him on the DPS charts (of course, then he also reforged for as much mastery as he could get his mits on. I pointed out how bad it was and the changed the next raid.
As for your DPS are you:
Hit Capped (or way over)?
Trying to get mastery? (a big waste for shadow priests, crit is 3x better and it's the second 'worst' damage stat)
Switching targets frequently? Shadow DPS in slow to start, so switching targets in NOT our thing.
Glyphed properly? (With the SW:D bit, you probably are)
Using Fiend whenever its up (on Bosses)? (Nice bit of DPS)
It's kinda hard to give a more full breakdown without your current DPS and what your gear looks like. 1-2k should be very possible starting, but seeing your gear would help.
If a group is getting on to you for using PW:Shield as a Discipline priest (or jeez even a Holy priest), you have my permission to say "GC says you're doing it wrong."
"What... What the h*** was that?"
"I think I just saw a mountain kick a castle."
-exert from Sengoku Youko