How can I stop my truck from starting without the key or getting under the hood...?? Can I pull a wire or a fuse.. ??

In the past you could have used a battery kill switch, but that can harm all the computer modules on cars today, so try pulling the starter relay or the fuel pump relay. If you pull fuel pump relay car will crank and crank but never catch. Are you worried about someone with a spare master key stealing the truck? Having to constantly pull a fuse or relay will get real old fast, maybe look into additional third-party anti-theft devices for your vehicle like lojack, GPS tracking, gear shift locks, etc.

Let it run out of gas.