with a cv your pinion needs to be 2* under the slope of the shaft. from my experience just 1* off is all it can take to have problems
the reason for this is because the pinion will rotate up towards the bed upon loading the driveshaft (acceleration). OP in your setup, when loading the shaft you are probably pushing the pinion angle further up and forcing the driveshaft to be out of balance. Balance is key and only a tiny miscalculation in a shaft can cause a good vibration.
