Drivetrain Problems?

[f150harley]

I need a little help on figuring out what could be wrong, I have a 98GT
5 speed. When I'm driving and let off the gas i'm getting a bad vibration then when I give it gas it make a clunk noise but the vibration goes away.

Any ideas where to start first?

 

[02wingless]

Pull your driveshaft loose and make sure the u-joints move freely.