8 1/4 to 8 3/4 driveshaft changes

Like fishy68 said, it looks like it needs to be longer, not shorter. Normally, there isn't enough difference between the 8 1/4 and 8 3/4 to need a new driveshaft but it looks to me like your old one wasn't long enough to begin with. Maybe that was some of the vibration problem you had.