That 3" exhaust is probably hurting your power a good amount. Even a fully built N/A motor doesn't need a 3". Unless you have future plans of turbo, you should really downsize that exhaust. 2.5" will be more than sufficient.

Like Dave said, a set of cams, intake manifold, and a tune will net some decent, usable power. I'm still using the stock TB at around 300 whp, so I doubt you are having any restrictions there.