Oil Pressure reading

[win717]

I'm having an issue with my oil pressure. After warming up my truck (2001 Dodge ram 1500 with 360) the oil pressure would drop to zero and when i would rev it up the oil gauge would go up so I replaced the sending unit and now it just reads zero no matter if I rev it or not. I decided to purchase an oil pressure testing system. The pressure at idle is at around 10 psi and at 2500 its reads at 40. What should it be reading I have no clue