dk/war + 4 rets / 4x rets or 4x dks + holy paladin

Hey there,

I'm running either dk/war tank with 4 ret paladins or 4dk / 4 ret paladins with a healer, holy paladin or disc priest

I've seen topics here saying that a dk tank + 4 ret paladins is the best setup for heroics 5 mans, I'm not really understanding how as my team is freaking weak!

If I run a tank + healer + 3 rets or 3 dks the fos / pos normals ain't a problem, except the tunnel in pos which is a pain no matter what I do, its hit or miss.
I'm around 4k gs, my dps on bosses is 2-3k and on trash around 4k? with my paladins or unholy dk's.

So how do you survive heroics without a primary healer? how is this team supposed to work? I'm guessing having 2p t10 helps alot but unforunately I'm miles away since I cannot clear heroics and I'm pretty sure I can't queue into specific heroics to start with the easier ones.

Can anyone here help me push me into the right direction? I have no trouble healing and I think my rotation is pretty good but the healing doesn't seem to be enough so I must be missing something?

How should I gear up and how should I spec my characters? without a primary healer I can't even complete the FOS last boss even if I dodge his nasty beam, the healing doesn't match the incoming damage.

and running 4 rets or 4 dks with a holy paladin its much the same, the incoming damage if the damage spreads between different characters my holy paladin can't heal them up quick enough with flash of light before one or two dies. Using Holy light does work sometimes but it happens occassionally the character dies before the heal goes off.

I'm sorry if the text is abit confusing I don't know what I should ask for so general advice is much appreciated, thanks alot in advance!