Hello and welcome to justanswer.
Does the speedometer work while driving?
The engine control computer does also control the transmission. There is a connector on the transmission itself that could be unplugged. This connector is on the front side, facing the radiator. #7 in picture below.
Thanks for the picture, the plug appears to be locked in and in good condition. I unplugged and checked the connections on the computer and they all appear good. All pins straight etc. My parts car is a V6 would it hurt to try that computer and see if transmission problem goes away?
Here is the schematic.
PCM Connector C3 Blue
There is no switch on the shifter, the transmission range switch (neutral safety switch) is located on top of the transmission. This is likely the part that was replaced.
Here are the schematics for that circuit. At the PCM use the connections noted for VIN T.
PCM Connector C1 Black
PCM Connector C2 (Gray or Clear)
Park/Neutral Switch Connectors