Why won't my new brushless system go faster?

Okay so I bought a Traxxas stampede complete 1/10 scale model with the titan motor and what not. So I thought I'd upgrade the motor and esc with the fuse 1/10 scale 5800kv brushless system to go faster. I installed it and programmed it, but the old motor seemed to go faster then the fuse brushless system. Any ideas? Do I also need to upgrade the battery? Or the pinion gear? If so what do I upgrade it to?