Oil Pressure loss!!!

This is a wierd one. New motor, .030 360, no exterior oil leakage, starts up and goes to 80+ psi. Begins to warm up and drops to around 60. At idle drops again to around 30 increased RPM does not affect the drop in pressure. Pressure increases and decreases at random and soon drops below 10 psi. New oil pump drive shaft, no change. New oil pressure guage, no change. I will drain and check the oil and filter next for debris and water. Any ideas????