A good way to figure out if you're uncrittible is to hover over your defense rating in the character sheet and check what percent crit reduction you have. Same level mobs have 5% base chance to crit you, your pally has 3.8%. For each addition level they outlevel you there is an additional 0.2% added. The level 70 needing 490 is against raid bosses(3 level higher).

Also, my healer is a priest and I have a castsequence macro with Prayer of Mending and Renew bound to the same button as my dps' spam button. As soon as my dps start casting, my priest hits my pally with a PoM followed with a Renew and sits there until PoM is ready. I have Flash Heal, Greater Heal, Prayer of Healing, Circle of Healing bound to other buttons in case I actually need healing. Is there a skill that shamans have that's on a fairly short cd so you're not spamming heals on your tank but also allow you to prevent spike damage? My experience with shaman healing is 4x chain lightning. :P