If it's the last character (the last letter, like 56029914AF vs 56029914AG) then it's the same part number, just a later version of it. Regardless, all 3G hemis use the same 545RFE trans. In fact, if you use the donor trans with your existing PCM you will need to perform a quick learn as your PCM has the clutch values for your original trans and not the new one and run the risk of damaging the donor. 2500 PCM's have been hit and miss with behaving in a 1500 chassis. If you try it, you have to flash the new VIN, the original programming may not match your truck options and if you have SKIM key, that will need to be initialized to the new PCM, which will require a new module (once a SKIM has been initialized to a PCM it cannot be mated to another).
My recommendation is to use your original trans (unless it has problems) and go the local tune out route.