Changed oil pump on 2003 Toyota camry runs fine then loses oil pressure what is wrong with

Is this high mileage vehicle? If so, I doubt changing oil pump will help, you may need engine overhaul?
Sometimes, you use an analog pressure gage in place of the oil pressure sending unit, to read actual oil pressure. My info says at idle, oil pressure 4.3 psi or more. At 3000 rpms, it says 43--78 psi.

I would suggest a second opinion. It sounds kind of high.

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This will help.

Thanks.

check transmission fluid level.if fluid level okay, transmission fluid and filter been changed. code scan for ecm faults.sound like problem in the transmission torque converter.leaking valve body gasket or faulty valve body and bad oil pump losing pressure not enough oil pressure to get transmission in drive or over drive.

check to see if your oil filter is tight

The engines oil pressure switch has a third wire which is connected to the fuel pump. The oil pressure gauge may work although the third wire to the pump may be at fault causing your delimma
Once the engines oil pressure reached the normal operating range the computer shuts down the oil switches third wire to the pump and the relay takes over until you shut the emgine off

A lot of It depends on the condition of your coolant. or the percentage of coolant vs water.
50/50 is best. Too much coolant wont cool as good. Too much water and the lubrication and protection is lost. Then the waterpump goes out from lack of lubrication.
The water pump can also go out from the driving belt being too tight. Whether it is driven from the timing belt or a serpentine belt or a V belt.

bad to worn out oil pump or excessive oil passage clearances that allowing more oil to pass thru them at a lower pressure due to the bigger opening. It can be a sign of an emminant engine failure due to oil starvation.

it sounds like your oil pressure sending unit may be plugged by whatever took your pressure down to 5-8 psi the first time. this is extremely low pressure as i am sure you know but at 30 psi your light should go off i would replace the sending unit if your oil pressure is holding 30