Driveline vibration above 75mph.
 

I have a drive line vibration that starts just above 75mph and just gets worse. I did not have this problem until I installed my T56. When I was running running my T10 the transmission was angled down 3deg and the rear end is angled up 3deg and I had no vibration. Now with the T56 the transmission is angled down 2.5deg and the rear has not changed. The driveshaft is new from Strange so I don't think it is the problem. I'm wondering if the longer transmission at 2.5 deg and the shorter driveshaft all combine to cause my vibration. Any advice would be appreciated,

I think you'll be surprised how much a 1/2 degree difference will make... Put your car up on blocks so it can set at ride height and reset your pinion angle. That "should" clear it up.

Well the pinion angle was not the problem. The transmission was angled down 4deg and the pinion was angled up 3deg. I raised the transmisson mount 3/8" to 3deg down angle and went for a drive. Ran it up to 105 and the vibration is all gone. I agree it is amazing how a small adjustment makes a big difference.

Good to hear you got it resolved. Another gotcha is a lot of people do not index the trans to the bell housing which can cause vibration and eventually failure to pilot bushing, issues to trans input shaft wear, strain on bearings, gears etc.