You might want to look into ground clearance.... I know TCI makes a REALLY deep one. You can also use a GM truck pan. The deep pan is not needed, however anything that helps dissipate heat for the trans (fluid and surface area) is good.
Well I believe in keeping the trans cool. If GM makes a trans cooler that will bolt on to the GTO, I'm going to get it. Also the way I see it anything you can do to help prolong the life of a Automatic Trans is a good thing, especially with the expense of a rebuild or a new unit. For me that means a trans cooler, a trans remote filter kit and maybe a deep pan.
I do hope to maybe someday install a new camshaft and possibly a new torque converter.