it really sounds like your dps is the issue, we 2tank pally/war and 3heal priest(holy)/Pally/druid or shammy and we push chogall after 3 adds on 10man... were able to leave 1 dps on chogall full time and get the add down just as fester comes and have no problem with the oozes, and when the 4th add spawns you hold it off to the side move out of shadow crashes and have the tank interrupt the AoE