I can't guarantee that this will help but it sounds like something called the Chrysler Creep. I had a Siemens VDO Dayton nav system in my Saab 9-2x. The VSS was connected correctly, but the positioner would tell me I'm moving when coming to a full stop. Turns out the VSS signal needed to be modulated. I purchased a sine wave converter that was essentially a square wave converter and used it to filter the VSS signal. Cured the problem instantly.
You may want to ask a professional installer if they've seen this happen with the Pioneer AVIC's.
