My 94 chevy 1500 has a problem. When i speed up fast or take a sharp corner fast then start driving the truck makes a sound like your hitting the rumble strips until you let off the gas.

2 wheel drive or 4? sounds like a basic drive train universal is shot. under load turning or accelerating you get the vibration, unloaded(coasting?) you do not...? wheel bearing can cause a similar situation. have you checked them? put the truck on a lift and look for leaks in area of wheels/axles might help isolate the location of problem...my two cents!

simple but often overlooked...check lug nuts to ensure they are tight!