I don't have a good answer for you. I can agree that it's not realistic for the pinon on a street-driven JK to point up to the TC. That said, most aftermarket DS's offered for a JK are, unexplaneably, DC shafts. Most of the time owners aren't getting the driveline vibes you're seeing. I have a 3.5" lift and run bout 5 degree caster on that PR44 Unlimited axle, so my pinion is up about 5 degree (for reference) and I don't have issues with my DC shaft. I ran this same driveshaft on a factory rubit axle with about 4.5 degree caster (~1.5 degree pinion angle) with no vibes. The only thing I could suggest trying is raise the caster a bit (lower the pinion) and see if the vibes change.