As far as i know, the only replacement PCM for the GT is the Digital Horsepower chip from Intense. In addition to removing the 105 mph limit, it does a few other go-fast upgrades like different shift points and remapped fuel/spark tables.

http://www.3800performance.com

Hope that helps. There isn't much you can do besides replace the chip, so this seems to be your only solution.

ferb!