Your vehicle could be shaking due to a suspension component being worn out, for pickups it can cause a "death wobble" this is very specific to a certain suspension system, but when it happens it can be dangerous due to the lack of control you have when driving. If this happens you need to hold the steering wheel firmly and slow down as quickly as is safe while still in control of the vehicle. You may have to come to a complete stop for it to go away, once this happens you can start driving again. This will keep happening at unpredictable times until the suspension issue is fixed.
Give us a call and let us take care of you.