FWIW, I hooked up my scan tool to the OBDI port and it shows a operating system of 55491998.
Vin # MMM156LMHH635XXX
I decided to download the EFI software and update the firmware on my V2 controller ( very old ) and read the tune on the 2.5L trail blazer.
I must say to EFI, that the software I havn't used in close to 8 years, is still very easy to use, with all the nice updates.
I guess I only have one last question, Is this operating system ok to flash? if so I will go ahead and purchase a new VIN license.