How did we get to Pluto so fast with decade old technology?

The new horizons travelled 3 billion miles at an average speed of one million miles per day. 19^th Jan 2006, New Horizons roared into the sky with a speed of 36,000 miles per hour. Its propulsion system included only 170 pounds of hydrazine propellant. It means journey is basically propulsion-free. So how? Once the new horizons entered earth’s orbit, it is barreled into the solar system with a heliocentric (sun-relative) speed of 100,000 miles per hour. At this speed, it was timed to pass Jupiter in 2007. As it was nearing Jupiter, sun’s gravity slowed the speed to 43000 mph. However the Jupiter’s gravity is so high that it pulled and helped new horizon to regain its speed to 53000 mph.  From Jupiter it entered interplanetary space and sailed it’s last long 7 years to reach Pluto with the average speed of 36,000 mph. It is a humans greatest ever achievement.