I had 5.3 Vortec engine and 4l60e transmission installed in my 63 Impala. Drive shaft was modified as result of going from 700R4 to the 4l60E. Carrier bearing was replaced and driveshaft was balanced. No problem initially but started getting bad vibrations mid car at about 60mph +. Had ball joints, control arm bushings, tire rod ends and shocks replaced after finding wear in these components. After this had front end alignment done. While car rides better, I still have the vibration. Any thoughts on what could be causing this?