Limping and code P1603

These may be separate issues, I just do not know or I am second guessing myself. Here is some background: Vehicle was purchased for our son, four maybe five years ago. Leak developed at automatic transmission cooling line and by the time it was caught the vehicle had been driven a quarter of a mile with no fluid. I am comfortable with a wrench so I decided to do the rebuild. Obviously put the transmission on a bench and split it open. In addition to some crispy friction plates I also found the thrust bearing at planetary sun gear toasted. I will attach a picture. Did the rebuild, reinstalled now vehicle slips in rev, I have power to the wheels in drive but trouble shifting. It is also throwing me a code p1603, back up battery fault? Am I dealing with separate issues?

Additional: Trying to sort out this p1603 while I wait, is my ECU and PCM the same part with different names? And is it located under my passenger dash?