i need your help!

[69mychevy]

hey everybody june 30th i posted a question that looked sumthin like this: my 69 chevy sometimes will vibrate at 445 or 50 and sometimes not until 65, how do i fix it, is it u-joints?? driveshaft?? i hav to go on the highway with this truck and i can't when its vibrating, and its not at high rpms when its vibrationg only like 2000

i got a lot of answers but i don't think many of them are right because it is in such a range of speeds and rpm's so it couldn't b u-joints or driveshafts could it? if it is tell me, if not tell me what u think it is