When you raise the line pressure the throttle pressure also rises. Since the governor pressure has to overcome throttle pressure in order for the upshift to occur, raising the line pressure will raise the shift points (all else being the same).

Failure to downshift at a complete stop can be either a stuck shift valve or a faulty governor....only to tell is to hook up a test gauge to the governor pressure test port; anything over 2 psi at a standstill is a faulty governor.