This depends on when your pickup is shaking. Is it at an idle? Driving down the road? Town speed? Freeway speed? When cornering? I know, so many questions. In order to properly diagnose the issue you're having it's best to be as descriptive as possible as to when it does it, where it does it, how you're driving when it does it.
Now to answer at least one of those. When you're driving down the road at any speed and your pickup starts shaking it could be a U-Joint on your driveline. U-Joints wear out over a period of time and it this goes un-repaired it can lead to further damage of your driveline components and could in the worst case scenario cause an accident.
Give us a call and let us take care of you.