Not sure but i am currently dealing with a defective NSS. As part of the repair I had to tighten the bolts holding the shifter pivot.

Explanation: There is a pin from the shifter that sits in a plastic arm inside the Nuetral Safety Sw. if there is too much play the pin will slip in and out of the arm and it will cause the electrical connection inside the switch to not engage. Also, there is a shift interlock device inside the case as well with the NSS and shifter pivot. It sounds like they might not be interacting correctly.

Recommendations:

1. Get the Bentley's Manual - you'll see that advice time & again in these pages
2. Remove the shifter cover and look for the conditions mentioned above. You can actually see the threads to 2 of the bolts but you have to do a little contortion (no pun) to get to them from the underside.
3. You can remove the shift interlock with no appreciable damage to vehicle and drive it that way - When I opened my cover my interlock was already removed - much to my dismay at not being exactly like it says in Bentley's.

HTH and I hope that this finds you well in CO