So i’m ordering a New PCM for my 02 5.9 and i ordered the same part number PCM as my old one but i’m just curious as to was the different part numbers are as they go to the power train like mine has “AD” at the end and some have “AC” or “AB” and some begin with “5L”

 

The two letters at the end are just the revision number. Maybe some minor improvements made to the hardware over time. Still functionally exactly the same. The Prefix though, that, I don't know.

 

I had a 2011 Grand Caravan that the fuel pump relay failed in the TIPM. We bought the lifetime warranty on that van, so after I figured out the problem I gave it to the dealer to fix. They put the new tipm in there, but when we drove it home the front turnsignals didn't work anymore. Long story short, they ignored the directions to repin the connector to accommodate the new tipm. A dealer tech on the forum clued me in, and I had to take it back in and tell them what they did wrong. Even after I showed the the copy of the first page of the directions, they still couldn't figure it out... then blamed me for not printing out the entire directions (which I never had)! That was my last warranty purchase, the relay was $5 from digikey and it would have cost me less time than the time I spent dealing with the dealer for the first trip.

Anyway, getting the same part number ensures its hardware is exactly the same. Different revs in theory shouldn't matter, but in some instances it might.