GMC Repair: vehicle vibration, drive shaft, force balance

Question
I have a 2002 gm 3500 box truck. Only when driving I hear and feel vibration, fast bump, bump, bump... When driving at a crawl I feel a small grind sometimes. When driving all speeds can feel vibration, but when I accelerate and keep accelerating it goes away or is not noticed. But as soon as I let off the gas, it returns.

Answer
Hi
Really hard to diagnose vibrations. If you have the tires balanced (I would recommend a Road Force Balance). If the vibration still exists It may be that you'll need to have it diagnosed at a shop. We use a special tool (EVA) which pinpoints the frequency of the vibration in turn the area to look for the fault.
Tires and wheel are though the most common areas. Drive shaft is next.
Just my opinion.
Hope it helps.