Is this fight in 8man HM like.. really off?
We've gotten to him twice now and both times we've hit a wall. Compared to videos I have seen from Suckafish's kill
Found your problem.
But seriously, it's entirely possible you're getting blown up because of itemization. My alt PT survives him just fine and I did hardly any NIM TFB/SV on him. Maybe you're using too many high endurance enhancements or mods.