Jdb510

I’m having this issue. 08 Suburban 5.3. My oil pressure dropped to zero. Replaced the sensor and had pressure then bled down to zero after a short drive. Replaced the oil pump next and a new oring in the oil pickup. Had great pressure for a week then gauge stated reading 40 at startup then stayed 18-20 psi. It had bleed down to zero once and then I got a P0521 code. Replaced the sensor again and same readings. Now I have hooked up a direct gauge at the front of the motor and now show a 20 psi diff from direct garage to cluster. The cluster shows 20 psi at idle and the direct shows 40. Driving direct shows 52 psi and cluster just above 20. I clear the codes and it keeps coming back. What is my issue???? Any help is greatly appreciated!