Replacement drive shaft, Trying to cure vibration

[Rich84]

I have been chasing down a vibration since a rear gear change from 2.56 to 3.73. Thinking it might be the driveshaft or ujoints, I went to my friends junkyard looking for a replacement. They had several 3.66" aluminum drive shafts off of crown vic police interceptors. It measured exactly the same as mine from center of the joint to center of the joint (55.5). Some conversion ujoints from NAPA, and it went in perfectly.

It helped a lot but I still have a vibration from about 55-62mph..I think what's left is probably from the 15 year old tires.

Anything else I should be looking for???