The Stovebolt Site Forums The Shop Area Driveline Pulling u-joint for first time

The reason why you don't want to put jack stands under the rear axle housing when disconnecting the torque tube & tranny connection.
Is because the rear axle on 1/2 ton trucks are attached to the leaf springs using a spring seat with a bushing. Picture
The spring seat allows the rear axle to rotate on the leaf springs. Its not a solid connection.
Putting jack stands under the rear axle, makes the front of the rear axle and the torque tube rotate downward.
Putting jack stands under the rear leaf springs would prevent the axle from rotating but is not a stable lifting point.

The purpose of the axle to rear spring seat bushings is to dampen out road noise at its source and in doing so,
prevents it from telegraphing through the springs to the frame into the body.
Also eliminates any axle to spring binding when the springs compress/decompress.
1948 - 1951 Chevrolet Truck Shop Manual Rear Spring Seat

While you have it open up you should check to see if there is any play in the propeller shaft inside the torque tube.
Wiggle it up down side to side.