[wiswind]

There are a lot of things that can cause this......
1 thing that jumps out is the lack of speedometer when the problem happens.
Do you have the mechanical speedometer (needle that physically moves) or electronic?
If mechanical.....there is something wrong with the physical drive for the speedometer cable......on the end of the vehicle speed sensor......which has a mechanical connection for the speedometer cable AND a electronic connection for the PCM.
For the electronic speedometer......we are still looking at the vehicle speed sensor.

If the vehicle speed sensor is not working......the PCM does not know how fast the vehicle is moving.......so it does not know how to shift the transmission.

The Vehicle Speed sensor is mounted on the back side of the transmission.....roughly the middle point on the motor/tranny assembly.....right above one of the catalytic converters.

Another thing that can cause problems with shifting (that is not inside the transmission) is the Transmission Range Sensor......also known as Neutral Safety Switch.
This can go bad in 1 or more positions........
The TRS tells the PCM what gear you have selected with the gear select lever in the vehicle.
There are LOTS of connections inside that small box.
The TRS sits on top of the transmission......the cable from the gear select lever connects to it.