Lets call the rear diff portion of the equation, the pinion. I think I understand the pinion it pointing up. You need to know the angle at trans to front shaft. The angle from front shaft to rear shaft and angle of rear shaft to pinion. The three angles should add to zero. I.E. +3 deg, -3 deg, 0 deg = 0. You need to read the internet re: Two piece driveshaft angles and get a good understanding without the shops numbers. Then see if the shop numbers make sense. If the front shaft is level, then the rear shaft is treated like a one piece driveshaft, equal and opposite angles is desired. 3-4 deg is the number to shoot for. You are right about the torque-up of rear diff. The rear shaft and pinion should be set up so that torque-up moves angle towards zero not towards increasing the angle. If I see your explanation correctly, you are way off. Shims are your choice but reweld is better. Would flipping the leaf springs do anything? I know it's a pain but you would have the axle off it less than two hours.
