Well you'd have to remove the transmission, pull off the torque converter and open up the front of the transmission to see what the damage might be. So, not exactly a DIY operation in your driveway. The problem with opening up an automatic transmission is the "while we're in there" situation---the transmission is out, much of it is in pieces, and so patching it up internally without a full rebuild could turn out to have been a waste of time and money.
Answers
How do you know the pump is the problem?