How do I fix the oil pump drive shaft on a 1995 Dodge 318 truck? The truck keeps loosing oil pressure even after I have replaced (new) the oil pump. I am at a loss of what could be wrong?

The drive shaft isn't much more than a hex shaft that goes between the distributor and the oil pump. In most older engines the oil pump is driven by the distributor.

What exactly is the problem? Loss of oil pressure or no oil pressure. You might have problems elsewhere.