Lazy macro question

[suicidesspyder]

Ive been looking everywhere reading everything and i guess i just dont get it. Ive tried the whole

/targetenemy [noharm]
/cast [noform] !Shadowform
/castsequence [combat] reset=0.5 0,1,2,Shadow Word: Death
/castsequence [combat] reset=0.5 0,1,Halo
/castsequence [combat] reset=0.5 0,Shadowfiend
/castsequence [nochanneling] reset=target/19 Shadow Word: Pain,Vampiric Touch,Mind Flay,Mind Flay,Mind Flay
/castsequence Mind Blast,Mind Blast,Mind Blast,Devouring Plague

This actually locks up at points and i dont have the slightest idea how to break it into swap action bar macros. Everytime i try it doesnt work at all. Now ive gone to the below macro but it seems like devouring plague seems to not cast cept once every three or four casts after it procs.

/targetenemy [noharm]
/cast [noform] !Shadowform
/castsequence [combat] reset=0.5 0,1,2,Shadow Word: Death
/castsequence [combat] reset=0.5 0,1,Halo
/castsequence [combat] reset=0.5 0,Shadowfiend
/castsequence [nochanneling] reset=target/19 Shadow Word: Pain,Vampiric Touch,Mind Flay,Mind Flay,Mind Flay
/castsequence Mind Blast,Mind Blast,Mind Blast,Devouring Plague

Any help would be great just want to get this set so i can increase my dps on my priest and then test it out on other toons.[/FONT][/COLOR]