DPS help

[Nomial17]

So my issue here is that I have a lot of trouble hitting the 18k DPS mark consistently, on a lot of fights im lucky to reach a stable 16k dps. Now I know that given my gear I should be hitting higher than that consistently but I cant seem to pin point what im doing wrong exactly.

My armory is http://us.battle.net/wow/en/characte...krayonz/simple
and my rotation is as follows

Shadow Bolt (Shadow/Flame Effect)
CoE
Haunt
CoD
UA
Corruption
Shadowbolt Filler

I use Soul Swap on the adds in Cho'gall, do the same for the phases with Magmaw, yet my dps shows no real improvements despite my best efforts, iM kind of posting this as a last ditch effort to maybe find the reason as to why my DPS is so low as it is.

[Naturae]

From what I can see...you're not demo and you're not spamming hellfire on Cho'gall and Magmaw.

[Shadocaster]

From what I can see...you're not demo and you're not spamming hellfire on Cho'gall and Magmaw.

I would like to add something to this. I personally have gone Demo on cho'gall and magmaw, but the little buggers aggro to me and 1-2-fuck-you me if I go into melee range.