Finish each of the four parking levels to unlock an additional parking level. Finish the bonus parking level to unlock a sixth parking level.
Hold X and press Start at the title screen. Keep X held until the mode selection screen appears. Choose any mode to drive the Nippon Maru truck. Alternately, successfully complete arcade mode with all four characters.
Successfully complete the game with all five trucks (Asphalt Cowboy, Stream Line, Long Horn, Highway Cat, and Nippon Maru).
Successfully complete arcade mode with all four characters to unlock two bonus trailers in score attack mode, versus mode, and arcade mode (if the Nippon Maru is selected).
Go to arcade mode and select any truck. Get to your destination ahead of your rival , then complete the bonus parking mini-game to win bonus parts. This works on any destination.
For Highway Cat and Stream Line, shift up when at about 50 mph.
When you are behind a truck, your size you will get a slip stream. This will allow you to get a small boost to get in front of the truck.