Welcome. Unfortunately this forum isn't as active as other Buick forums so you probably won't get too many replies.
Officially, the GS tranny is rated at exactly what the stock tune puts out. Several of us are running a tune that bumps power around 70whp/tq without issues... but obviously haven't run them more than a year to know if there are long-term tranny issues.
I suggest checking out the other buick forum if you want a more lively discussion