A common problem with your truck is the fuel pressure regulator goes bad, pull the vacume line of it and see if there is gas coming out of it. If gas comes out its bad. Let me know
Im glad you found your problem, I have reread your question several time, and It sounds
like there were several issues, first off the transmission not shifting properly and no overdrive,lack of power, black spark plugs tell me running very rich. The first that comes to mind is a bad or missing ground to the PCM as this is one thing PCM and the Transmission share. Because you stated the previous owner had installed various accessories. I don't know if this the answer but its where I would have started.The whole point is to try and figure out how I could have helped you from here. Sometimes this isnt easy to do but I do try very hard and have been successful in the past. Just so you understand If and when you use Just answer again, you need to know that you are never required to pay for an answer until you are satisfied and find it useful and even then its up to you. You should not have hit the accept button 3 time as this charges you three times. I have requested that you get a refund and I suggest you follow up on it as well. I don't do this for the money, I do this because I like trying to help people. Im sorry that we got off on the wrong foot.
PS Please dont hit the accept button again.
Yes it has to be the same number as it is programed to run your specific engine values. You can buy PCMs rebuilt and there just as good as new. If you can find one in a salvage yard just make sure its same make and model along with same engine.. Ford goes by calibration number for replacement.