I realize that there may be several failures that can cause this issue. An easy answer is always the manual release under the steering column however if you would like your vehicle to operate as it originally did, you must determine whether it is the shift lock solenoid at the bottom of your shifter that is the culprit or if it is the wiring coming from the solenoid leading up to your ignition switch. I have a 2002 blazer with the same problem, after I removed and jumped the pink and yellow pins of the connector going to the lock solenoid the key did release. This told me that the wires and ignition were good. After that I tried replacing the shifter assembly, that did not work either. So the only variable left was the connector itself. Come to find out, commonly there is nothing wrong with the solenoid or the ignition switch or the wiring, it is just the connector. The pins inside become so stretched that they will not make contact you can either replace the connector or buy a pin removal tool to remove the pins and bend them back into the correct shape to make contact.