Car Rolling in Park??

I was going to suggest the linkage that goes from your shifter to your tranny. There is an adjuster on the rod to the tranny and if it is too far one way, your tranny won't engage in park. You may put it in park with the shifter, but the tab on the tranny won't be far enough in park to engage, therefore slamming the shifter into park might just put that tab just far enough into park to stop it from rolling. Hope that made sense.