A warlock that knows what they're doing can outdps a DK that no idea.
Locks need to balance hit from gear, hit from talents, raw SP, and depending on your spec, crit and haste. Are you hit capped with talents? Are you logging off your lock with Fel Armor up?
And what kind of guild are you in at this point that wouldn't carry someone at your gear level? Seriously, two runs through Naxx25 would fix any gear issues. If they're still "progressing" through Naxx, why would they take an app that is below the level they need for raiding? Not being allowed to raid by your guild for gear reasons seems absurd to me...

and even 1667 spellpower isn't very good. try running a few more heroics.

LOL @ 1343 SP.

You do know that you are asking to be carried if your spell power is that low. Not saying that they shouldn't carry you, but if your raid is having trouble clearing it themselves your not helping with numbers like that. Wait till you get at least 1600 sp completely unbuffed before you even ask again.

1343? Do you have all open gem sockets and no enchants? That's.... REALLY low.