How many miles on the car/tranny? If there is any significant milege on it, I would suggest maby getting a soft parts rebuild. Putting a shift kit and/or stall on a old tranny usually kills it rather quickly. My Camaro has the stock tranny with 105K miles on it. Everyone tells me, and I know from experience, that a stall makes such a huge difference, especailly on those cars because it has a very tight converter, and a cam, so it needs one. I know if I put a stall on it, I'll be rebuilding the whole tranny within a year most likley. Then again, if your hard on it, even without a stall, your probally going to kill it anyways, so I really don't know what I am trying to say.
If your going to get a differnet converter, the first thing I would do is put on a tranny cooler (B&M supercooler) flush the trans, put in a tranny temp gauge, maby a better deeper pan, put in a new filter, maby a shift kit, then do the converter. I would suggest a 2500-3000rpm stall speed. Get a lockup converter so it will be just like stock when cruising, but comming off the line, it will really wake up. If your only going to be on the street, 2500 should do, but if you plan on going to the track much, 3000.