Because 2000 was the cross over year for TheftLock Radios, try this:
1. Turn the ignition ON (The Delco radio displays "LOC or INOP").
A. If your radio says INOP, then you have entered too many wrong codes. You will need to leave the vehicle ON for 1 hour or turn the key into the ON position for an 1 hour, before you can proceed to Step 2.
2. Hold down the preset buttons 1&4 or 2&3 for approximately 10 seconds.
The radio display changes from "LOC" to a three-digit number.
Write this number down.
3. Press the AM/FM button.
The radio display changes to another three-digit number.
Write this number to the right of the first one.
Post the numbers back here and I can get the UNLOCK code for you.
IF there is NO numbers that appear, then GM Dealer will have to UNLOCK / Program the New Radio
Let me know what you find