89 Bronco Oil Pressure Issues

I have a 89 Bronco, Eddie Bauer edition. 302, 5.0 V8. I keep losing all oil pressure, I have been through the oil pan, replaced the oil pump, cleaned the oil pick up, and replaced the oil sending unit. But for some reason when I first start it up the oil pressure is normal but when the engine warms up and I press on the break and the engine drops below 1500 rpm it will lose all oil pressure and the red engine light comes on. Any suggestions would be greatly appreciated.

My first guess, crank/push rod bearings worn out. As oil warms up and becomes thinner, it flows quicker out from these areas and drops the pressure enough to set off the warning light at lower rpms. If it was mine I'd try a thicker oil. But most likely you need a rebuild soon.

You could put in a high volume pump if there is one available.