18 Wheeler - American Pro Trucker cheats and cheat codes for Gamecube

Unlock extra parking levels
Finish all 4 parking stages

Unlock 6th parking stage
Complete the bonus 5 parking stage

Unlock Nippon Maru
Jump to the title screen hold X, after push Start. Keep holding X until,
you will see the Mode Selection screen. Choose a game mode, to unlock
Nippon Maru.

Unlock Lizard Tail
Finish the game with all 5 trucks, including the extra car: Nippon Maru.

Unlock in trailers in Score Attack, Versus and Arcade mode for all trucks:
Finish the arcade mode with all 4 characters.

Get bonus parts
Complete the parking mini-ame, afterwards defeat your opponent in
any Arcade race.