Vibration?

i have a 1989 377 that I have owned for many years and it has a vibration hop at 60 mph that I can't get rid off. I have changed ride height, new drums new shocks? Michelin tires and I have centramatic balancers on all axles and it will be fine then it starts to vibrate and hop and it gets worse until I speed up or back off. Could it be drive shaft? It also has old style bud wheels. I need some ideas please.

 

Seat shifter cab everything but steering wheel. I have a feeling it's the old style double nut bud wheels. I will put it on blocks and spin the tires when it quits raining. I just put new drums so will the fit if I change hubs and rims to unilocks?

 

I have owned this truck for 10 years and it has done this before and after brake job. It has also had 3 sets of tires on it and it has hopped with all of them. I have also used balancing beads and now centermatics. On the odd occasion it will not do it then turn a corner and it feels like your driving on a washboard. Thanks for replies

 

I also own a 06 379 and drive the same roads with it, it's like riding in a stretched limo compared to the old girl. I should add the 377 has newway rear suspension that has been added later in life. Thanks again

 

How do you check for wear? I have had a safety done at two shops into the last 7 months and it seems they didn't let anything go.