[SulkierLizard]

Did you imply that the additional key won't work if it says PK3M? I thought that might be why I'm having trouble since it's two master keys. I tried what you said, but the security light stayed on solid while I was in Park. I was able to drive, though, which was weird. I'm not too sure if I want to switch to that key with the security light staying on. Should I go buy a PK3 key with no M on it?

I also tried this fro my manual:
To program the new key:
1. Insert the black master ignition key in the ignition
and start the engine. If the engine will not start, see
your dealer for service.
2. After the engine has started, turn the key to OFF, and
remove the key.
3. Insert the key to be programmed and turn it to RUN
within 5 seconds of removing the original key.
4. The SECURITY light will turn off once the key has
been programmed. It may not be apparent that the
SECURITY light went on due to how quickly the
key is programmed.
5. Repeat Steps 1 through 4 if additional keys are to
be programmed.