He is my primary healer. I do have a cleric but I only put him in the group when things are too much for Shammy to handle.
This statement does not compute to me. I don't raid anymore, so I'm only ever in group gear but without Redguides, as a SHM with 13K hours, if I'm geared with just the best group gear, best current augs, max AAs, I can easily out heal any CLR that isn't the best at their class and raid geared to the current expac. I can never be convinced otherwise.
Now with that being said, I assume you're running him through RG, ideally you want every single AA maxed, but if you're just using them for healing & plus the slow and debuff:
Prioritize
General: (I don't upgrade any of this stuff at first)
Archetype:
Abundant Healing
Healing Adept
Healing Boon
Healing Gift
Malaise (Lowers targets resistances)
Mastery of the Past (so you don't fizzle spells)
Mental Clarity (Mana Regen)
Mental Stamina (maxes mana pool)
Wind of Malaise (Pretty much Malaise for when you get 1 or more adds and the tank is suffering)
Class:
Cannibalization
Soothsayer's Intervention
Turgur's Swarm
Turgur's Virulent Swarm (for adds to group)
Union of Spirits
Focus:
Spiritual Swell
Ancestral Intervention
Reckless Regeneration
Luminary's Synergy
I feel like that will pretty much keep you covered with healing in a group. Also make sure to have all of your current spells for expac and level. And for god's sake, do the epic up to 2.0 or he's basically worthless.