Is the shift interlock difficult to replace yourself? I assume it is in the console under the shifter?

 

Hmmmm..?? Wish I knew and could tell you, Tony, but I don't know for sure if it's mechanical, electro-mechanical or completely electronic?

 

Sounds like you may be in need of a new shift selector assembly.

-Sheldon.

 

Disclaimer:
I hate automatic transmissions with a passion. Before we got married I insisted that my wife-to-be converted from automatics to stick shift, and boy, it was touch and go! Now, nearly thirty years later, we've got two (mostly) delightful daughters: and guess what? They are confirmed stick shifters too!

For what it's worth, get under the hood and look on the transmission for the selector switch linkage; you may find it is connected to the console by a cable (like a bicycle brake type cable, believe it or not)!
If this is so, there are a few problems which arise from wear between the inner (moving part) and the outer fixed jacket. The transmission loses its indexing between the gates on the console and the switch assembly on the tranny, and can do some crazy stuff. Fortunately this can be fixed because the cable is adjustable at the tranny end, and can (tediously) be re-indexed to the console gates.
The other thing which can cause your problem is that your transmission "thinks" that the handbrake is not on, and there is a safety interlock between the tranny and the handbrake which prevents shifting out of park (to stop the car from rolling).
I'm not certain how its hooked up, but if the handbrake signal is missing, you can't get out of park. So start by locating the switch on the handbrake assembly and see that it's adjusted and working properly.
And if that's not enough, there's yet another damned interlock between the tranny and a relay on the ignition switch which prevents removal of the key if the vehicle is not in park. If your ignition switch assembly is worn, the contact which tells the tranny that there's a key in the ignition may not be working, in which case the "brane thing" (which in reality is mostly a mess of switch contact, relay logic, with the odd fuse thrown in for good measure) thinks "OK, there's no key in the ignition, and I'm in Park: so I'm cool with that."
Before delving into that, you could try using your spare key and see if the ignition switch is the culprit.
Dumbassed damned bloody automatics, I hate 'em, ALL of 'em!!!

 

The level of autotrans.. work is much higher now.

 

Very clever inserting that link in there as you did, bonapart1.
Do it again and you are gone from here.