Yoke phasing

I have a quick question about yoke phasing, but first some background...

I've been chasing an oscillating vibration on my car since I assembled it that starts in gently at around 2500 in high gear and gets progressively more intense the higher up in RPMs I go. I only feel it when I'm cruising along on the highway and it'll rattle your teeth at 4000. If I'm running WOT, either it's lessened or I just don't notice it because I'm busy.

I recently took the shaft into a local driveline shop to have it checked and get the U-joints replaced and I noticed the yokes on the shaft are visibly not aligned. Not severe...maybe around 5 to 10 degrees, but enough to notice just eyeballing it. I asked them about it when I dropped it off and told them about my issue, they told me "don't worry about it".

Well, the shaft is back in the car with fresh joints and the vibration is exactly the same as it was before. I've tried changing the pinion angle and added/removed shims under the trans mount with no effect on the vibration.

Could the yokes be the issue? My engine/trans mounts are only a couple of years old and, eyeballing from the rear, it looks like the pinion is in line with the transmission. I could try swapping the center section or borrowing a set of tires, but I've been through the tires before with no luck.

Thanks for any assistance.