For the curious and fellow NOOB's...

I finally got a chance to install my spare ECM. All went as planned. Here's what I did.

Swap out ECM's:
1. Disconnected BOTH batteries.
2. Removed plastic cover from box that housed the ECM.
3. Disconnected 3 connectors from ECM: Blue, black, grey.
4. Reverse above for installation of new ECM.

VATS RELEARN:
1. Crank engine - It may or may not start. (Mine did not start.)
2. Leave key in ON position - not accessory. (Security light will turn on.)
3. Wait 10 minutes for SECURITY light to turn off. (My light turned off in 7 - 8 minutes in which time I went to step 4.)
4. Turn key OFF for 30 seconds.
5. Repeat steps 1, 2, 3, and 4 two more times for a total of three times.

My truck started after three sequences of CRANK-wait-CRANK.

Thank you everyone for your help!