I am looking at the longest attempt I saw with you healing. It was a 7:22 length try: http://www.worldoflogs.com/reports/6qz02dfqj4kf8rd1/details/1/?s=4698&e=5140
So I'm going to start with your talents, specifically, selfless healer. Selfless healer is a weak talent for holy paladins in the best of cases, and this fight is definitely not the best of cases. I see you only built selfless healer stacks 5 times over the entire attempt, and you seem to have sat on them for a while in at least 2 cases. Finally, when you do use them you have >50% overheal with your casts.
With a constant raid damage aura and combos lasting for 10 in a row instead of 5, assuming your tanks are doing their jobs correctly tank healing is less intense on heroic then it is on normal. The difficulty comes from keeping the raid up at the same time as tank healing, all of which point to eternal flame being a much better choice. Pick up eternal flame and divine purpose, and focus on your hopo generation and blanketing, and will see a dramatic improvement.
Also, your cd management could use some work. I only see you using avenging wrath once, and you didn't use divine favor at all. The damage intake on Hwill is very smooth for the most part (raid error excluded) so you should be regularly cycling through cd's in order to keep up your output. Don't be stingy, you are more likely to oom yourself keeping up without cd's then to let someone die because you didn't have a cd for emergencies.
Finally, I would recommend clemency over unbreakable spirit, although both are a valid choice on a fight this length. I really like the freedom it gives me to throw hand of sac at will on tanks, spark soakers, etc.
Edit: I noticed this after I posted, but you have the 4pc (hs cd 4sec) but over the course of the encounter you had 56 hs casts. That pencils out to an average of 7.9 sec between hs casts, which is really long. HS is your primary hopo builder and should be used as close to on cd as possible. Make yourself a weakaura, or get some way to visually track the cd in an obvious way...mine is a massive holy shock icon right next to my raidframes.
Edited by Corvala on 2/5/2013 11:35 AM PST