Driveshaft Length

Just wondering if anybody else has a correct drive shaft, but seems too short, after measuring center to center length on car, I know it should be approx 1" shorter, but mine is 2" - 2.25" shorter.

I have a 360, 727 trans and 8.25 rear.

All of these components came from the same donor car (less motor).
I believe the drive shaft to be correct at 45" center to center length.

After multiple measurements my center to center on the car (under weight of vehicle) is approx 47 1/8".
This leads me to believe I need an additional 1" on shaft or 46"

Trying to remedy a bad vibration starting around 50 mph and gets worse up to around 65.

Just dropped the shaft off at a local shop and waiting for a price to re-tube.

Has anybody encountered this before?