Do you have a Holy build that is working well for you in 10/25 instances? Mind sharing a link to it?
My Holy build isn't working, I go OOM very quickly. My first response is going to be putting 3 points into Meditation, and a 3rd into Concentration. It is so bad that I am performing much better with my disc build simply for mana reasons.
If it's not my build that's the culprit, maybe my rotation. I'm casting Renews, lots of Flash's, keeping up PoM, using PoH sparsely, and the occasional Guardian Spirit or CoH. I rarely am casting Greater Heal, Binding Heal, Holy Nova, or Divine Hymn.