you need download the calibration file from GM onto the TECH II, and dealership doesn't run TIS2000 or use the TECH II anymore. i think they've been using GDS2 (laptop scantool) for over a decade now. not sure if they can help you or would even let you if you had a tech ii.
this guy runs through how to do it on a couple of different vehicles (non GTO). I guess he has TIS2000 running on a PC in his garage, and i think you need a subcription to Acdelco TDS to use it.
it would be wise to just find someone who already has these legacy tools that can help you.