The shift plunger on the left, rear side of the valve body has a notch or groove which needs to be engaged (mated) with the shifter mechanism as the valve body is reinstalled. If you didn't do that previously, it is possible that the plunger was damaged as the valve body bolts were tightened. Also make sure that the throttle plunger aligns with the cable bellcrank on the right side. (That usually takes care of itself.)

I recommend that you verify proper shift mechanism operation before reinstalling the pan. (Have a helper move the shifter while you observe from below.)