Where am i going wrong, i have 2 pieces of T10 (1 is Sanctified), rest of my gear is from ICC25 and POS/HOR/FOS and got the Abysal Rune/Nethermelting Ice Crystal for trinkets

My rotation is VT>DP>MB>MFMF>SWP>
Then MB>MF>MF and refresh any dots

but for some reason i my dps in 10and 25 man's is only 2500-3500
i just cant seem to get any higher than this no matter how much i try.

i have quarts installed to stop me from clipping but i hear all these shadowpriest boasting about how great their dps is and im ranking in the middleground.

Can some one suggest any addons which might help or if i need to respec my rotation.
I also have Shadow Timers installed to alert me when dots need to be refreshed.

any advice would be great