Ford: 82 Ford Mustang Gt 302HO 4 speed..., ford mustang, mustang gt

Question
Hi,
I just wondered if you had an idea about what I am experiencing. There seems to be a vibration down the middle of the car when driving. I feel it in the seat, wheel and underneath all around me. I did change the U-joints last summer and didn't mark the driveshaft when I took it off. If I installed it 90 degrees off, would it make a vibration because of that? Or something like the driveshaft needing rebalancing?
Thanks for your input.

Answer
It can very well make a vibration because of that. is it an automatic or a manual? If it is a manual did you replace the clutch when you took the driveshaft off have seen this where the clutch has added to a balance concern. will the vibration happen if you rev the engine with no load? or is it just speed related?

Please let me know

Jim