Chevokeeman

I bought a 1997 Grand Cherokee to fix up and tow my bass boat with. I changed out the bad 5.2 engine and got it running, tryed to take it for a drive and it seemed to be slipping very badly so I pulled it back in and checked fluid level and it was fine. Next I changed the filter and gasket which looked new with no residue on old filter or in the bottom of pan. I called the transmission shop and they said to take the cooler lines loose at the cooler so I did and there was no fluid coming out at all. I suspected the pump gear might be broken so I pulled the pump apart and checked, it looked new with no wear, I'm stumped at this point, any suggestions???? Chevokeeman.