.
Your ‘51 Chev PU needed a new fuel pump for the wipers to work under a load.
The top portion of the pump was a vacuum booster that was capable of keeping the wipers operating, if its diaphragm was not ruptured.
.
Wipers ran off manifold vacuum pressure. When it dropped, on acceleration or under load, the wipers slowed or stopped. They didn't run from the fuel pump.