During a race or Free Roam mode, type goldfinger. After you the confirmation sound,
press [Ctrl] + Y. The game will pause. You can now move your truck freely. Use the 
[Cursor Keys] to move forward, hold [Shift] to drive fast and [Alt] to slow down. 
Press Q to go up and A to go down. Press [Page Up] will twist your vehicle and 
[Page Down] to twist it sideways. You can also press K to control other vehicles.