A833 Vibration Issue

my guess would be the tranny needs rebuilt

if it was the pressure plate/flywheel/etc it would still do it in neutral. pressing in the clutch pedal might make it go away.

but yours does it in 4th at highway speed, then goes away when you push in the clutch and shift to neutral. almost would bet it's the input bearing.

there are some trans experts on here wait for them to chime in.

also check the runout on the bell housing like fklskv recommended