As suggested by "71yelladustr" its best to scan it and drive it with the scanner as you can have someone go and watch all the inputs and outputs to see just what is going on. Even better if you can data record it. I used to data record all the sensors when I had driveability type problems as it lets you look at them when you get back in the shop and dont have to try and diagnose it while driving the truck. And you can take your time to watch and see if the PCM demands OD and if the PCM tries to ground the OD solenoid. That way you can see if the PCM is asking for OD and if the PCM is grounding the OD solenoid. It will also help you tell if its an electrical or mechanical problem. Also you may want to clear that code and drive it as I got fooled once when there was an emission code in the PCM and it would not let the overdrive work until I cleared the code. Sometimes when the PCM has a certain emission code it can keep other circuits turned off if it thinks it will effect emissions. That code should not but as I said I thought the same before and found out the PCM would not ground the OD solenoid to work with certain codes. Good luck with it. Ron