Nippon Maru
Hold X and press Start when you are at the title screen. Now keep X held until the mode selection screen appears. Then choose any mode to drive the Nippon Maru truck. Or just Finish arcade mode with all four trucks.

$999 by hitting bonuses
Hit a bonus head first, then press L1 + R1 + X. You will receive the maximum amount of $999. Note: This has to be repeated each time.

Lizard Tail
Finish the game with all five trucks (Asphalt Cowboy, Stream Line, Long Horn, Highway Cat, and Nippon Maru).

Bonus parking levels
Finish each of the four parking levels to access an additional parking level. Finish the bonus parking level to access a sixth parking level.

Bonus trailers
Finish arcade mode with all four characters to access two bonus trailers in score attack mode, versus mode, and arcade mode (if the Nippon Maru is selected).

Hints & Tips

Bonus parts
Go to arcade mode and choose any truck. Then get to your destination ahead of your rival, then finish the bonus parking mini-game to win bonus parts. Note: This works on any destination.

Slip stream
When you are behind a truck, your size you will get a slip stream. This will allow you to receive a small boost to get in front of the truck. As a name input ACO in championship mode, then return to the main menu.

Shifting
For Highway Cat and Stream Line, shift up when at roughly 50 mph.