1999 Dodge Durango Oil pressure

My 99 Durango with a 318 V8 is completely dropping oil pressure. I have just changed the oil pump and cleaned the screen. Drove it to the store and still dropping pressure all the way to 0 psi. While your driving down the road the pressure is normal and up around 40psi but when you come to a stop at a stop sign or something it drops out. Then you hit this accelerator to take off and oil pressure goes back up to normal. Any help will be greatful! I have to leave from Texas to be at work in Virginia in two days!