badboy- ya,

The extra gears are for the center-differential. The truck comes with a locked center-differential. The center locked diff will enable the truck to pull wheelies, but it has been found that it puts more stress on the truck's drive-train. Most people have been installing the center-differential for this reason. The center differential will make the truck handle much better through rough terrain and sweeping turns. Thanks for your question badboy- ya.

Kind Regards,
CEN RACING