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"Bricked" PCMs usually happen due to a failed flashing event, typically vehicle battery voltage goes low, the connection is interrupted, or there is interference from other modules (typically radios, etc).
If you're getting controller unlocker errors and you haven't even tried to flash it yet, try removing your radio, onstar, and transfer case fuses (if there is one specific for that module). This is most common on 2003-7 trucks in particular or if you have an aftermarket radio, etc.
If you did have a failed flashing event, don't turn the key off. Try the flash again and remedy any of the issues mentioned above.