The steering shafts do not need to be replaced because they are not strong enough it's because the coupler on the box end sucks and wears out quickly. Aftermarket kits replace it with a u joint setup.
RAMMAN4 said:I know that some of the 70s trucks used a reversed setup where the rag joint was on the steering box and the coupler was on the steering column as opposed to the 81-93 style that uses the coupler on the steering box and the rag joint on the steering column.