My 2002 F-250 with the 5.4L will "sometimes" stall when I pull into a parking space and shift into reverse or park. Most times the idle just dips real low when I put it into park also. What is the problem?

 

I have a 2001 F350 that does that. For a while I had to start it in Neutral and then shift into Drive. Now I cant shift into reverse at all. As soon as the shift indicator gets to the letter R the engine stalls. I had a cracked half clamp on the shifter shaft, which I replaced.
Any idea what's causing this problem?