Hello, I have a 1995 Nissan Quest. Low pressure when the engine is fully warmed up.

Hello, I have a 1995 Nissan Quest. Low pressure when the engine is fully warmed up. Oil light comes on and engine lifters clacking. After start up when cold the oil pressure is fine, but the lifters do clack a tiny bit. Oil level is good and filter is new. I removed the oil pan and found allot of sludge in the pan. I removed the oil pump and the oil pump gears appear to be in good shape with no excessive wear. The relief valve and spring seemed to be ok. Do you think it could be the sludge in the pan started to plug up the inlet screen, bad oil pump, or excessive bearing clearances? I am considering replacing the rod bearings and maybe the oil pump. Thanks for the help!