don't forget to add

/cast !Rune Strike

at the end of your DK macros, it will auto swing Rune Strike every proc, and RS is a huge part of DK threat generation.

btw I prefer tanking as blood since the gear requirements are less (less hit/expertise) plus all the self-heals that blood DKs get is very nice in multibox situations. A prot pally however is much better still for a multiboxer, due to less incoming damage and team buffs.

This is my DK blood tank macro:

#showtooltip
/startattack
/castsequence reset=target Icy Touch,Plague Strike,Pestilence,Blood Strike,Scourge Strike,Death Strike
/cast Blood Tap
/cast !Rune Strike

I have D&D on a seperate key (not used by team), horn of winter is on the same key as my drop-totems, Vampiric Blood is on same key as group heal, Icebound Fortitude is on same key as heal tank, and I have a seperate key for blood DK self-heal (forgot ability name lol).