I am not sure this is possible, but you're barking up the right tree. You've gone backwards in terms of transmissions if I'm understanding properly. It's more than the VIN. This is a bit outside my comfort zone, but I would first try for the heck of it swapping the transmission computers-- the hp30 and hp30 tcm should be together, and the hp24 / hp24 tcm should be together. Am I following you-- you've got a 24 tcm and a 30 transmission installed now?
BTW- don't wipe your hard drive just yet- while the GM software will hurt you sometimes-- it can also help.
And for heavens sake- stay away from eBay GARBAGE Gt1!!! IF this is an avenue you want to pursue for coding / reading / diagnostics- PM me (if we can even do that as new members) and I'll point you in the right direction. I don't know if TOS allows for openly discussing that stuff.
It's not what you buy, it's what you build- Unknown
EN90283 - Stabled for HG repair
DH06247 - Running like a champ