vibration in body at 50-90 km/h - better when warm? not wheels/brakes/engine

I had the exact same symptoms as you. A 1-piece tailshaft fixed it. No vibrations to 200km/h now.

 

if the vibration is around 60ks most likely driveshaft, I had the same problem, ordered new 2 piece from nissan US, problem solved

 

OP, when you say not engine, does that mean if your standing stationary with the transmission in neutral; & you rev the engine when cold, there is no vibration issue?

I have a similar problem to you, were @ speeds >80km the vibration starts.
< 80k's it's fine.
However, once it warms up it goes away, except under full open throttle.

 

Yeah stationary its a bit choppy at idle once warm (slight misfire) but once you touch the throttle its butter smooth - not the same vibration

Throttle does not really change my issue, though.

I made an interesting discovering.

vibration wasn't too bad at the time (still present), driving along at about 40km/h in 1st then planted my foot, broke traction and got some axle tramp to 50/60 km/h and the vibration was IMMEDIATELY worse right after that axle tramp and then it sort of settled down 500 meters down the road.

further if I am driving in 5th at 1,200 rpm or so and then jabt he throttle I can hear metallic clanging and get quite a big of back-lash in the process as the the slack is taken up each way in the shaft - could be my diff/diff bushes arnt in very good condition either

Im currently investigating what to do about the shaft. I might get one made locally - getting one shipped with our current exchange rate is not a good deal.