Axles and related Driveshaft out of balance or bad u joint Bad trans bearings clutch/pressure plate throwout bearing engine mounts pinion lock nut backing out (bad rear)
Also, bad vibration/poor performance could be valvetrain related...bad springs?
Si Vis Pacem Parabellum
1967 Starlight black PMD Engineering 400 Auto 1968 Alpine Blue 400 4 speed 1968 Verdoro Green 400 HO 4 speed 2013 1LE 2SS/RS Inferno Orange Camaro.