I tested my car yesterday even though the burned out instrument cluster was missing . Since it provides information mostly I carefully cut the wires and killed the circuit at the fuse box.
During the engine replacement I drained the engine, torque converter, and cooler. I replaced the filter. I put Dexron Mercon III ATF back in, 7 quarts at least.

I put the car in gear. It was a little slow moving but I guess it took time for the torque converter to fill.

I drove the car for 30 minutes. It ran fine and the transmission shifted smoothly. I came home and parked it

30 minute s later, I restarted the engine and shifted and the car wouldnt even move. I think the tranny is shot. I checked the shifter linkage and its fine. Why would a tranny fail like this? I would think it should have failed immediately upon my driving the car...

Finally what does the big electrical plug on the driver side of the trans do? I think it has ...like 5 pins...the plastic snap lock isnt there so it may have come loose..