It is a great time to replace the drive shaft.Check the ends of the shaft and the internal hex of the pump drive, They make better drive shafts these days. My shaft and
oil drive were about to round out when I had my engine apart.They make a special pump and drive for trucks It has a 5/16" hex at the pump and a 1/4" at top for the distributor . I asked why only one end is larger and was told that the pump end is the end to always have a problem.
That would be a pump and drive combination. High volume= a taller gear and case , higher pressure = a shim in releif spring. I bought a blueprinted Melling high volume truck pump and driveshaft