That fits the symptoms of a clutch that has oil on it. Sometimes the rear main seal will leak & some oil gets on the clutch disc, causing it to chatter. Other things could be involved, like bad motor mounts, but in my world it has usually been oil on the clutch. If that is the case, then the clutch disc itself should be replaced, & the pressure plate & flywheel should be cleaned & possibly resurfaced/replaced depending on the condition. And the source of the oil needs to be fixed to keep it from happening again.
My buddies in high school called my 64 Sprint "Shake, Rattle, & Roll" due to this condition.