I had the same problems when I got to 90 and walked into my first heroic. It was beyond frustrating. My setup is Pally Tank, Priest Disc, Mage Arcane, Warlock Destro, Shaman Elemental. My solution was to grind daily quests out and hit the world bosses until i was able to get some of the justice point epic gear. It took a bit of time but i was able to make money and get all my Rep to exalted which was nice. My group is now around 490 ilvl from doing dailies and world bosses and i've been able to rock most of the heroics now with the exception of 3 where i've had problems due to the mechanics of the encounters, but I'm sure I'll get them as well once i learn how to do it. I also don't have a dedicated healer now and my priest is able to heal all the heroics through Atonement by doing DPS (she pulls about 30k DPS right now). The rest of my DPS is at about 50-60k each and my tank is pulling about 20k which is still low compaired to some people I see hitting 100k but it's about average DPS for most people.

Keep at it and you will get the heroics down and then wonder why you had so much difficulty.