Ignition key won't release even though shifter is in park position

It can't but two other things can....
1. The solenoid on the gear shifter.
2. The ignition solenoid on the column.

They work on tandem, the one on the shifter tells the one on the column to engage to release the key (allow it to turn to the off position) when it is in the park position. The one on the column releases the shifter when the key is anywhere other than the off position.
So it can be one of two things.
( most likely ) One of the wires on the solenoid on the shifter is bad and on occasion faults out an doesn't send power to the column solenoid and keeps the key from turning to the off position, thus keeping you from removing the key. ( a little less likely ) That solenoid itself is bad and it will cause the same issue.
( even more less likely ) The solenoid on the column has intermittent issues...

Possibly crawl under car and dissconnect the shifter and manually move the selector on the trans out of Park Position. Normally the locking feature is in the steering column.. which you can also take apart to release this feature.

The ignition key must be in the key cylinder for cylinder removal. The key cylinder must be removed first before removing ignition switch.REMOVAL 1. Disconnect negative battery cable at battery. 2. If equipped with an automatic transmission, place shifter in PARK position. 3. Rotate key to ON position.4. A release tang is located on bottom of key cylinder.5. Position a small screwdriver or pin punch into tang access hole on bottom of steering column lower cover.INSTALLATION 1. If equipped with an automatic transmission, place shifter in PARK position. 2. Position key cylinder into steering column as it would normally be in the ON position. 3. Press key cylinder into column until it snaps into position. 4. Check mechanical operation of switch. Automatic Transmission: Be sure transmission lever is locked in PARK position after key removal. If key is difficult to rotate or is difficult to remove, the shift lever-to-steering column cable may be out of adjustment or defective. If key can be removed, release lever mechanism may be defective. Release lever mechanism is not serviced separately. If repair is necessary, the steering column must be replaced. 5. Connect negative cable to battery. 6. Check electrical operation of switch.

sounds like the cable from shifter has loosened and is not moving far enough to register it is in park to allow it to release key should be a simlpe enough fix ,buti have not worked on one of those to help you further , alocal mechanic should be able to help u without too much hassle Good luck

Most newer models have a safety feature called
shift interlock. This prevents the key from being turned back
to the lock position if you forget to place the gear selector in park.
Depending on the model,
If it uses a cable, it may be sticking or needs adjusting.
If it uses an electrical solenoid. may be blown fuse or park switch.
Tap, shake, and pull up on the shifter and make sure it's in park.

Ignition - Key Stuck In Ignition Switch/Won't Turn Bulletin No.: 06-02-35-005 Date: February 28, 2006 TECHNICAL Subject: Key Stuck in Ignition, Key Will Not Return to Off Position, Shifter Button Won't Release in Park Position (Adjust Shifter Detent Finger) Models: 2002-2005 Chevrolet Monte Carlo Condition Customers may comment on any of the following conditions: - The key is stuck in the ignition cylinder. - They cannot return the key to the off position to remove the key. - The shifter button won't release in the park position. Cause This condition may be caused by the detent finger shifting over time. This may result in mis-alignment and binding of the shift rod on the shift position guide.
WHERE YOUR SHIFTER IS YOU WILL HAVE TO TAKE IT APART ..MAYBE THE RUBBER BOOT IS IT THE WAY,OR THE SHIFT LOCK SELINOID WHENT BAD

I have worked on several vehicles with this same problem and each one was a relatively simple repair with no parts involved, first off the shift interlock has nothing to do with it and will not prevent your vehicle from going into park, it is designed to work ONLY when coming out of park. The problem your having depends on the type of shifter handle your vehicle has, if the release lever is on the bottom and you have to push up with your fingers to release it, then the problem is...there is a rubber type cover that surrounds the release button, after time it becomes distorted and bunches up preventing the shifter from fully engaging in the park position (even though it appears the vehicle is going into park)if your careful you can work the rubber cover out and your problem is fixed. If your shifter button is on the side and pressed with your thumb the cable needs to be adjusted, this cables only purpose is to prevent key removal except when in park and is easily adjusted, with the center council removed, if you look at the front of the shifter base you will see 2 cables that snap into the shifter frame, the larger one is the gear selector cable, the smaller one runs up to the steering column and operates the mechanism that prevents key removal, where the cable snaps into the shifter frame is where the adjustment is done and is identical to a kick-down cable used on older vehicles with automatic transmissions, right where it snaps into the frame there will be a button you can press down releasing a spring loaded adjustment arm, make sure you first mark the arm for reference then press down the button and adjust it a little either way until it functions properly, hope this helps and good luck    

I have worked on several vehicles with this same problem and each one was a relatively simple repair with no parts involved, first off the shift interlock has nothing to do with it and will not prevent your vehicle from going into park, it is designed to work ONLY when coming out of park. The problem your having depends on the type of shifter handle your vehicle has, if the release lever is on the bottom and you have to push up with your fingers to release it, then the problem is...there is a rubber type cover that surrounds the release button, after time it becomes distorted and bunches up preventing the shifter from fully engaging in the park position (even though it appears the vehicle is going into park)if your careful you can work the rubber cover out and your problem is fixed. If your shifter button is on the side and pressed with your thumb the cable needs to be adjusted, this cables only purpose is to prevent key removal except when in park and is easily adjusted, with the center council removed, if you look at the front of the shifter base you will see 2 cables that snap into the shifter frame, the larger one is the gear selector cable, the smaller one runs up to the steering column and operates the mechanism that prevents key removal, where the cable snaps into the shifter frame is where the adjustment is done and is identical to a kick-down cable used on older vehicles with automatic transmissions, right where it snaps into the frame there will be a button you can press down releasing a spring loaded adjustment arm, make sure you first mark the arm for reference then press down the button and adjust it a little either way until it functions properly, hope this helps and good luck   

I have worked on several vehicles with this same problem and each one was a relatively simple repair with no parts involved, first off the shift interlock has nothing to do with it and will not prevent your vehicle from going into park, it is designed to work ONLY when coming out of park. The problem your having depends on the type of shifter handle your vehicle has, if the release lever is on the bottom and you have to push up with your fingers to release it, then the problem is...there is a rubber type cover that surrounds the release button, after time it becomes distorted and bunches up preventing the shifter from fully engaging in the park position (even though it appears the vehicle is going into park)if your careful you can work the rubber cover out and your problem is fixed. If your shifter button is on the side and pressed with your thumb the cable needs to be adjusted, this cables only purpose is to prevent key removal except when in park and is easily adjusted, with the center council removed, if you look at the front of the shifter base you will see 2 cables that snap into the shifter frame, the larger one is the gear selector cable, the smaller one runs up to the steering column and operates the mechanism that prevents key removal, where the cable snaps into the shifter frame is where the adjustment is done and is identical to a kick-down cable used on older vehicles with automatic transmissions, right where it snaps into the frame there will be a button you can press down releasing a spring loaded adjustment arm, make sure you first mark the arm for reference then press down the button and adjust it a little either way until it functions properly, hope this helps and good luck  

while in park, press shifter firmly even farther above park. Hold shifter and turn key.
The linkage may need adjusting. If this does not help the situation, then the pins inside the ignition are not getting pressed down because key is getting worn. You can try to tap around the ignition lightly with hammer to shake the pins loose.