Sounds to me that you have a battery drain--something in your system either has a continuous drain or there is a short. You can take your truck to any garage and they can check the battery/alternator, but it does not sound like that to me. Try doing a search here for clues on troubleshooting voltage drains to help determine what it might be.
A couple common drains are stereo/amp, sometimes brake lights/running lights, clock short, stuff like that. There are techniques to narrow it down, it has just been so long I can't remember...