I'd be surprised if a cam bolt kit would be able to change your pinion angle enough unless it just needs a very small adjustment.
What I'd do first is verify where exactly this vibration is coming from. Remove your rear drive shaft, shift into 4-HI, and go for a test drive to see if the vibration is gone. If it's not gone, you know it's somewhere else. You can also remove your front shaft and go for a drive to see if it's causing any vibrations. Once you are able to say with certainty what is causing the vibration, the fix should be more apparent.