Flow builds up too slowly, maybe make "berserker stance" and "signet of rage" work with it.
Flow depletes too quickly in order to build up in between mobs in PvE.
When in the burst stance, your stance cancels if you move; maybe it should just take 3 extra seconds more to activate the burst instead of rooting the warrior in place.
Damage is underwhelming; at full flow you should do something like 14k because of the difficulty of pulling it off.
When dual wielding, you should have access to your normal burst.
Dragon Slash requires 3 button presses to use!!!?
You've made conditions OP in the game yet this spec is severely lacking.
One of the burst skills could be a multi strike hit.
Will you be able to change the look of the gunblade?