What led you to replace the BCM?
Do you have a Tech2 scan tool?
Did you do the necessary programming of the BCM?
I would more comfortable with a Tech2.
Interesting about the UEC environment identifier.
The one thing I have always done when replacing BCMs, PCMs, CIMs etc is to note setup, config, etc.
Can you do things like module presence check;
High speed, mid speed, low speed can-bus config with your scan tool?
Yes, Tech2 can software update any module in this vehicle.
You also need to have access to the GM website for SPS programming.
Typically Tech2 is used for request current software from the vehicle.
It is then connected via an RS232 lead etc to your laptop.
Can be difficult to get this sort of stuff, if you aren't a GM dealer though.
How did the customer clear his codes, and was it running prior to this?
Seems odd this has all happened after clearing codes.
That Tech2 looks like a good deal.
Way cheaper than they were near 20 years ago.
I would say there is a wiring fault common to all three faults.
Can you open a new question since I have no info on that vehicle.