The Stovebolt Site Forums The Shop Area Driveline Vibration, rumble in driveline

If you was racing with sticky tires, then yes, your builder is right, but an everyday truck will not twist the axle that hard in any driving condition.
As a simple test, put the park brakes on and have a couple helpers push and pull the truck while you watch the pinion angle. If the springs are soft, it will rotate quite a bit.

Go back to equal angles and see how it acts.