That's because we, shops, other than a GM dealer , don't have the ability to reflash. Dealers charge , $175 to reflash plus any diag time ($100) I have a Mobil person with the equipment do mine! Again , it sounds like you may have more than one problem. I also have never replaced a Throttle body that wasn't a Delco part.
Most likely gonna bite the bullet and go to the dealership, maybe if they determine it was a bad TBS i can get my money back on that one. Can't try my old one (it was a core)....