What would cause a 96 2.2 Chevy S-10 to lose oil pressure after replacing the oil pump After the truck runs for a few minutes the oil pressure drops?

hello, this is common in high mileage engines due to worn crank bearing clearances etc.., heated oil is thinner than cold oil and flows easier ---- thus pressure drop, try a thicker oil and you'll keep the pressure high a little longer but eventually the only solution is to replace the worn engine