Had the same thing happen to a man in town whose fan clutch had gone out.
He went to a wrecking yard to get another. Put it on and it would cool around town, but not on the highway.
When he finally brought it to me, I had him start the engine and it was trying to push me away from the front of the truck.
His was a serpentine set up, the clutch and fan he picked up were from a standard V belt set up.
