What would cause your truck to vibrate at all speeds more so upon acceleration?

If your truck is rear wheel drive (which it almost certainly is), you probably have a badly worn U-joint (universal joint) in the drive shaft, which will eventually come apart leaving you stranded with a big towing bill. This will vibrate at any speed, and much worse as you acclerate, but might let up as you ease off the gas.

In any case, no matter what the cause, you should have it repaired by a technician before you have a more serious problem.