it will be your new driveshaft locking up on the inner cv cup, does the vibration get worse when turning right?
these longer driveshafts are of no use unless you are running massive negative camber. a standard driveshaft with uprated engine mounts will be fine. if u are that concerned about the driveshafts pulling out then fit some adjustable tcas to correct your suspension geometry, car will drive a lot better & it will save u wearing out your front tyres