Losing Oil pressure

Anyone had/have this issue. I am running a 360 mostly stock with 20w50 oil I have excellent pressure at start up, around 60-65 psi. Once I start cruising around and the car warms up it stays around 40-45psi. Problem occurs when I stop at a stop light, oil pressure drops to 10 or sometimes below. I normally put the car in neutral if I get stopped at a light and the pressure will stay around 15-20. Any ideas?