[wiswind]

It 'could' be the linkage and Neutral Safety Switch (aka Transmission Range Sensor) are not aligned correctly with the transmission.
When you move the shift lever, you move a cable that connects to the Neutral Safety Switch that is mounted on top of the transmission.
Inside the switch are many contacts that indicate what gear you have selected and the computer energizes the correct solenoids.
There is also a shaft that goes down into the transmission from the Neutral Safety Switch to engage the parking pawl when you move the gear select lever to the PARK position.

So, as it is know to be a high failure item AND is easier and cheaper to deal with.....I would look to the Neutral Safety Switch first.