Sticky valves in the VB... I bet if you take the effort to pull it, clean it and replace the check balls and the little 'button' it will help. I imagine that for the parking lock to engage at speed, it would need to be able to move 'on' to the notched wheel... and that would take some non-factory persuasion, i.e.
1) has the console been out or
2) is there some debris or damage to the linkages somehow underneath, perhaps a stick is caught up there somewhere...