18 Wheeler: American Pro Trucker Hints for GameCube
All you have to do is complete Arcad mode with all four characters
Successfully complete the game with all five trucks (Asphalt Cowboy, Stream Line, Long Horn, Highway Cat, and Nippon Maru) to get Lizard Tail.
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.
When you are behind a truck, you will get a slip stream. This will allow you to get a small boost to get in front of the truck.