What is a down hill thrower? I would think given the elevation of the mound, all pitchers are down hill throwers?
Downhill typically in the point of follow through. A downhill approach means that you release the ball and bring your trailing leg towards homeplate. It leaves you with a flat back (to a degree), it keep the momentum towards home (which forces the pitcher to release properly), and sets the pitcher in a proper defensive position.
Gonzo slides slightly towards third base. Not every pitcher, but most end up crossing their bodies and mechanically it can load too much pressure on the shoulder. It is something that should never be taught because it can lead to poor consistant command, but it also can lead to nagging injuries.