2000 GMC Sierra Engine will not start

Did you have the computer programmed yet?

Did you have a security problem with the old PCM?

That's true. It's leading me to believe there is a problem with the new PCM.

Partially. Your just repeating the 10 minute procedure 3 times. The light still needs to act the same way.

Here is the 30 minute procedure

30 Minute Re-Learn Procedure
1. Turn ON the ignition, with the engine OFF.
2. Attempt to start the engine, then release the key to ON (vehicle will not start).
3. Observe the SECURITY telltale, after approximately 10 minutes the telltale will turn OFF.
4. Turn OFF the ignition, and wait 5 seconds.
5. Repeat steps 1 through 4 two more times for a total of 3 cycles/30 minutes ( the vehicle is now ready to relearn the Passlockà † Sensor Data Code and/or passwords on the next ignition switch transition from OFF to CRANK).
Important
The vehicle learns the Passlockà † Sensor Data Code and/or password on the next ignition switch transition from OFF to CRANK. You must turn the ignition OFF before attempting to start the vehicle.
6. Start the engine (the vehicle has now learned the Passlockà † Sensor Data Code and/or password).
7. With a scan tool, clear any DTCs if desired (history DTCs will self clear after 100 ignition cycles).

No, you have another problem. The code is for "Ignition coil control circuit low voltage.

I'm giving you the flow chart for that code but I don't believe in that much of a coincidence. I suspect this has something to do with that computer you put in assuming you didn't leave anything disconnected in the engine.