Start the car in park first and then go right to nuetral, then go through all the gears and back to reverse and wait for the transmission to kick into gear. Make sure your level is right at the add 1 pint line when running cold.
I had the same problem and found the o ring on the filter was not seated correctly on the valvebody causing the transmission to suck air.Make sure you got enough fluid.
Your fluid should not look milky unless he used the wrong band on your drum.