i resored and converted a 1972 chev c-10 long bed from manual to automatic trans ,350 3 speed. ever since then at about 45-55 miles per hour i get a vibration. the drive shaft was cut and rebalanced to fit. the front end has been alighned and the tires are new and balanced.i measured and centered the carrier bearing and lined up the u-joint yokes. but i still get the vibration. the whole truck vibrates not just the front end. any ideas would surely be appreciated. thanks.

Check your wheel balancing.

Well my 71 had a bad rear end and it felt just like that was fine all around town but up to speed it would heat up and rattle your teeth out,also is it a one piece drive line or two????

i would go out and get you driveshaft remeasured if you dont find out the problem. if your drive shaft is to long or to short you are going to have problems and bad vibes. when is the vibe happening??

Get ur wheel balancingin place, I guess it shud work