If one used PCM did not work, my best guess is that is because there is nothing wrong with your present PCM.
Twice in my life I have had a car diagnosed as a bad PCM, the first time, an independent shop assured me the stalling problem I had was a bad PCM. His price was quite high and I lacked confidence in him so I talked to the Chrysler dealer and they said they had refurbished PCMs in stock and they could install one to see if it solved the problem and swap them back if it didn’t and only charge me labor. Either 1/2 hour or 1 hour depending how long it took. The PCM made no difference.
The second time was also for stalling but this time it was intermittent with no apparent pattern and the diagnosis was bad distributor (obviously different mechanic). The distributor was replaced and after a week it was obvious that that was not the problem. The shop owner claimed that I had needed the distributor but now the PCM was bad also. The Chrysler dealer rescued me again, he confirmed that the other car I had used the same PCM to see if the problem followed the PCM. It did not. I traded that car in and about 6 months later found out the problem was icing in the electronic feedback carb. under certain weather conditions.
So far, I have never had an actual computer failure. I am not saying it can’t happen but both of these places instead of doing actual diagnostic procedures, said, because it was not X, it has to be the computer. I never want to hear “it had to be the computer” , I would listen to " The computer is bad because there is no output from pin # x and there is power to the computer and I have checked the ground.