Pinion angle

If you have a smartphone Tremec has an app that measures driveline angles. Super easy to use. It also has calculators for engine RPM based on gearing and tire size, tire size calculator, etc. Pretty handy, probably not quite as accurate as if you have magnetic angle finders but it would definitely tell you if you're in the ballpark to the point that you shouldn't have any vibrations.

https://www.tremec.com/menu/tremec-toolbox-app/

Like everyone else said, there are a lot things that can cause a vibration and pinion angle is only one of them.