Park/Neutral saftely switch

I have a 1999 Malibu 3.1. Im having an issue with my car that seems to be boggling. After replacing several parts that I have verified were bad, the original problem hasn't gone away. But at idle and startup, it runs better than ever. I have a matco scanner and Snap-On Vantage but neither read tranny codes or test procedures. The only code it shows is an insufficient flow code for the egr valve. Which is blocked off. No biggie there. The problem that it's having is it stalls while cruising or accelerating. The fuel pressure was low so it has a new AC Delco pump in it. Now the pressure is within range. Mass Airflow reading are perfect, Map sensor reading are perfect, Coil output is perfect, alternator output is perfect.
Hear the kicker. I can't remember the code number right off hand, but in the freeze frame data I found a failure code for the park/neutral/safety switch. Which threw me off guard because I didn't think my scanner would catch that. Aldata states that this can cause erratic timing, stalling, etc.. and gives procedure for testing it.
Has anyone else ever had a problem with the park/neutral/safety switch causing running problems?
Thanks, lilwhitelude