Stupid high speed vibration

Update: The driveshaft shop found out that my yoke was twisted. This in turn caused the driveshaft to be out of balance. Mind you this is the same shop that built, installed, and balanced the assembly for me last year(car hasnt be driven since last year). Kind of weird that it wasnt found when they built it 6 months ago....oh well at least it was found. Yeah!!!
Also installed my new gears, went from 3.90 down to 3.27. This was mostly for drivablility but also to move the vibration up a few MPH if the driveshaft wasnt bad.

So in summary to solve the Tremec vibration problem in my car I had to push the tailshaft of the tranny up as high as it would go without hitting the tunnel. Verify that the driveshaft is good and in balance. Reset the pinion angle to match but opposite of the tailshaft angle. In my cause I needed adjustable upper control arms.....My tranny came out to be 3* down so I set my pinion at 3* up.
Notes:
-A vibration in the shifter was caused by the front of the driveshaft be out of balance
-A vibration in the seats/floorboard was caused by bad DS angles(tranny/pinion angles off)
-Poly mounts made the vibration problem worse
-Having the transmission and pinion angles not matching made the vibration worse.
-Not pushing the tailshaft of the tranny up causes bad driveline angles making the problem worse.
-RPM and MPH vibration are not the same narrow down what it is before you continue
-The motor and tranny can be run with out a drive shaft (for a short period) with a cap in the end of the tranny.....this will verify if its a DriveShaft or rearend problem.
-If you can get the car on jack stands, this will help the troubleshooting. Start with the removing the tires, then go from there.

Thanks for all the input, I hope to have many vibration free miles with my Tremec/Mustang.
 
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Glad to see you have it squared away, but after reading your post a couple times it doesn't say for sure if your vibes are totally solved. ?

On jack stands, the car was smooth til about 130MPH w/o wheels/tires....after a long weekend of work and working on the car I was not into road testing it. So I still need to get it on the road a verify 100% but best I can tell its all good. :nice:
Ill do a final update when I get a chance to roadtest her.....