What happens if I ground my amp to my body instead of the frame of my truck?

Grounding electrical items to your body is never a good idea.

However, you could always ground it to the body of your truck......

Your truck body is grounded to the frame. You will be good

The body is fine. Most of the grounds in the car are to the body.

so true

Let's put it this way. If you've got power to the positive wire to your amp and you hold the ground lead in one hand and then touch the frame of your car with your other hand, the electricity passing across your chest from one hand to the other can kill you. Is that clear enough? There's enough juice to potentially stop your heart, so go ahead and try it. One less fool in the world won't be missed.

(Drunk again so early, Pilsner man?. You've apparently never worked as a paramedic and seen it)