oil pressure drops after engine heats up on 1995 Chevrolet 1500 Pickup

truck runs good till you take it for a ride then oil prssure drops and engines sounds rough just bought it. Any suggestions about what might be the problem it is a chevy 1995 1500 pu.?

Asked by for the 1995 Chevrolet 1500 Pickup
poss oil pump or plugged oil p/u screen repl together
thanks for info will have them checked out!!!!