Wont work...Bad guys use stolen vehicles, and once the cop pursuit stops, they go out of sight and bail on foot, or jump into other cars etc, etc...
If pursuit can be eased back without fear that the individual will be completely lost, while giving the police an ability to intercept the car even after the contact is lost, the one fleeing would need to abandon the car for another ASAP to keep from being tracked—and the GPS would convey immediately when and where the car slows down to consider such activity. It may not solve everything, but it does seem like a useful tool in some instances.
Why not track them via the GPS in their Obamaphone?
Or peel the thing off and stick it to a passing bus.