ok first of all you shouldn't be gemming for armor penetration as survival(thats mm). Second, replace that str ring you have, its terrible just get the one with triumph badges. 3rd of all get 4 piece, its a good dps boost. With your current gear i would get the chest piece (but the best combo would be 4 piece no legs and use the ones from 25 lady deathwhisper). Your rotation seems fine but it also depends what you're doing during fights. As a hunter you should use every global cooldown, and as survival try not to clip lock and load procs (usually i wait until half of the duration of the debuff on the boss then i fire out another, also if i have aimed shot off the cooldown or the sting is about to run out i use them in between explosive shots). Hope this information helps.