My alt is a resto/enhance shammy. I feel like I know the class pretty well and I don't have any trouble healing...until my mana runs out. I keep water shield up as much as possible and use mana tide totem if i drop below half but fights like festergut and rotface still have me screaming for innervates long before the fight's over.
Here's my armory: http://www.wowarmory.com/character-s...mar&n=Bigtotem
Make sure you have replenishment. At your gear levels, you might have to go with some int gems, at high end gear you can afford to go full on haste.
Don't use offhands, use a shield. This allows you to put 25 int to shield. If you have access to ulduar still the one from XT drops fairly often, normal Pit of Saron has one, there's one each in both toc10 and toc25, and ICC25 marrowgar drops one too.
Energy siphon trinket is garbage for you. Grab the healer trinket from regular toc 5 man, tears of the vanquished. When you can hack it, halls of reflection has ephemeral snowflake, which makes you more efficient.
Make sure your water shield doesn't fall off EVER, that's a big one. Many a resto shamans forget to keep recasting it, and it costs no mana, just a GCD.
You seem to have a tank healing glyph setup. Pick either LHW glyph or ES glyph and replace with Water Mastery Glyph, 30% extra mana is pretty big. I'm assuming you run your mana spring totem instead of a non-imp wisdom or an ele/enh shaman's mana spring. Use your mana tide totem more often (When you hit 60% mana, pop it). Mana pots, use them more often. Ask for innervates, Power infusions, hymn of Hope (if somebody does hymn of hope, drop your mana tide totem at the same time, the combined effects are more than the individual ones).
For me, Rotface/Fester really comes down to how well ALL of your healing team is working. These days, we're in full ICC 10 gear and there's a massive buff; I barely break a sweat on Festergut or Rotface. Initially, though, I would frequently be scraping the bottom of my mana barrel by the end of the fight, partially due to over-extending myself.
For me, my mana concerns always come down to how much I'm trusting the other healers to handle THEIR assignments while I handle MY assignment. It was really hard for me to realize that I CANNOT get through BQL unless I trust my disc priest and resto druid to handle the raid while I play fake-paladin chain healing the tanks. The tanks weren't really taking that much damage, but if I used my spare time healing the raid (except when they're an inch from death obviously) I would run out of mana and be unable to do my job. In LK, which we're still working on with limited success, I really want to heal the raid but I just CAN'T--I have to limit myself to healing 'my' tank and sharing riptide between the two tanks, except for very limited spot heals when we're struggling with an infest victim.
You can also use mp5 food and flasks of pure mojo to help you out with a bit more mana regen. Nobody likes to do it but sometimes you have to.
Most of the time the runs I heal on consist of me, a holy paladin or a disc priest and sometimes a druid or another shaman. I usually kinda switch hit, spending most of my time on the raid but assisting on tanks as needed. so for the most part I pick a tank and keep earth shield and riptide up on them, then chain heal the raid as needed, stopping only to drop healing wave on the tank if he drops too low too quickly, since normally i'll have the haste bonus on that spell up.
You seem to have a tank healing glyph setup. Pick either LHW glyph or ES glyph and replace with Water Mastery Glyph, 30% extra mana is pretty big.
It only affects the passive mana regen. So the glyph is a flat 30 MP5 I believe, not worth a glyph slot for a raider. ES and CH are the two mandatory glyphs for a Resto Sham, and LHW is a solid choice for the third one.