Well Salvador will get much better at it with levels, right now you don't have the skill points to do it too much. I find that I don't use gunzerk all that much really, it seems to be a very group dependent skill and doing it solo does tend to get you killed. Though with the right shield, like the Firehawk shield or really any of the Nova shields (especially the one that goes off at shield or health drop) because it works so well with being in the middle of everything.