What is the u-joint angle? Tailshaft to driveshaft and driveshaft to pinion ?
When the truck starts vibrating, is it in overdrive or direct drive?
If you slip it in neutral, does it continue to vibrate?
If you go faster, does it go away or increase?
Here is a guy that's been chasing a vibration for years,
https://www.jalopyjournal.com/forum/threads/so-im-learning-a-little-about-tires.1192479/
