Ignition key can't be removed - sometimes

2001 Pontiac Aztek - Often when turning the car off, the ignition won't turn all the way off and the key cannot be removed. Wiggling the key sometimes works, other times shifting back into gear and rather forcefully back to park allows the ignition to go all the way off and releases the key. We've had no trouble starting the car or turning off the engine -- just can't remove the key sometimes. Also, the locks should automatically unlock when the car is shifted to park and sometimes this fails also. Could this be a key switch problem or possibly a relay or some kind of sensor between the shifter and the switch?