It's impossible to chain heal when 4x death and decays is under you, each with a 20% chance to make you cower and interrupt you spells. You MIGHT get 1 chain heal off if you're lucky. Not even close enough to help with all the damage you're taking. Also, there are all sorts of diseases going on besides death and decay. Also, I have pestilence 4x on the ground, makes you go 50% slower. It's a death trap for sure.

I have 4x 80 shamans too, along with the 4x DKs. You can't move your guys out of death and decay because at least 1/2 are cowering, the ones that do get out get death gripped back in, and they are moving at 1/2 speed with pestilence going on.

Right now I'm all unholy spec. I like the ghoul pet and all the AOE stuff I get. That way it's not quite as bad if one of my guys is facing a different direction.

Right now, I spam this macro
/startattack
/castrandom [target=focustarget] icy touch, Pestilence, plague strike, blood boil, Scourge Strike, Unholy Blight, Death Strike

and I also throw in a manual death and decay, that's about it.