Dead-aim---- i think this should be a standard action.
As for power shot-- personallyy i believe it should be the bows crit modifier or the str modifier (whichever is lower) otherwise the sneak attack damage could be multiplied by 10..... i don't think there's any reason it should be able to do that
The sneak attack damage--- i think it should stack with other class's sneak attack (it isn't stated) however, when making a 30+ ft sneak attack, it should be limited to the sniper sneak attack.

That way the power shot deals: (1d#+str+enhanancement+5d6)x3 still very sizable, but not a (1d10+str+enhancement+10d6)x3 (or higher if you did a ton of multiclassing)

I love the class, in fact i was planning on making a ranged fighter type and i might use this class after a few modifications