We had pretty much the same problems so here are a few pointers:
- 2-heal it. Even if it looks tough, it's possible, actually everybody does it. You should also push all your raiders to come with an OS for which they are geared and that they can play satisfactorily. Typically our holy paladin goes retri on this fight and does very well (he stays on the boss).
- interrupts.
- tank the boss closer to center, and have everybody stack on him, that way your prot warrior shockwave should be enough to break the MC on everybody. Have the fire mage dragon's breath at the ready as backup. More than 2 seconds MC = fail, period. Anything above that is not tolerable. Tell your players with single target interrupts to macro /targetenemyplayer with their interrupt ability.
- interrupts.
- have your frost dk eat the fury of chogall and retaunt immediately (if your healers have issues keepnig the tanks up)
- interrupts.
- avoid shadow crashes. Tell your raiders to move out ASAP, I know I've been hit by it despite being far away from the visual effect. I think it registers your position at some point while falling, not at the time of landing.
- interrupts.
- drops the big adds in a line, to create a nice train of small adds: easier to slow, easier to pushback, easier to aoe.
- interrupt depravity 100% of the time, and interrupt anything else, really.
- if you are around 30% when 4th big add spawns, keep dps on the boss and try to push p2. If you reach p2 with big add up, it will despawn (warning: if Cho'gall has time to cast Fester Blood the small adds will not despawn = guaranteed wipe)
- interrupts.
- you should enter p2 with nobody over 20 corruption really.
- interrupts.
- start movnig the boss when he's around 30% because he will stop when casting some abilities and will not necessarily be easy to kite. Move him against a wall, so that tentacles don't spawn all over the place. Actually, tell your tank to move him INSIDE the wall, and I'm sure Cho'gall will still not be as close to the wall as you'd like
- interrupt the tentacles, or you will never get them down with 4 people with a -75% debuff to damage and healing.
- use all burst you have on tentacles, then switch to boss only when they are all dead.
Did I mention interrupts? I might have forgotten, so once more: interrupts. Everybody, all the time, with whatever they have, including class abilities, talented abilities, glyphed abilities, racials and even the kitchen sink if they have to.