[Pursuivant]

Isn't there a GURPS book which includes rules for Parkour?

That would have useful rules for moving quickly in urban environments.

In rural areas, Survival (Appropriate Terrain) skill should be complementary to Running or Climbing skill. In built-up areas Urban Survival might apply as well, assuming that you're on unfamiliar ground and are trying to find a particular "terrain feature" like a fence, fire escape, or door.

Acrobatics skill could be used for tasks like vaulting over an obstacle or doing a forward roll to quickly go under an overhang.

Don't forget to apply penalties to Vision and require occasional Vision rolls if light conditions are anything less than perfect. It's very easy to run into something, or trip, in the dark.