Newbie Question.....Hp & Torque gains...
you are right to focus on a converter. That sould be your first mod. Won't add HP but it will make you much faster. Next I would get a lid, catback (or cut-out), headers, an underdrive pulley and some drag radials. Besides draining your wallet of several thousand dollars, these mods will make your car much faster, although your HP level will not be near 400.
I would not invest in gears unless you are looking for a specific combo (e.g. SuperYank 3500 converter & 3.73s) nor I would buy LS1edit or aftermarket tuning until you determine that you really need it. Tuning gains are generally small with a near stock motor and can be achieve through cheaper means such as a MAF translator or HPP3.

