Your oil pressure guage is it the factory gauge? Do you trust your guage?
Have you install a mechanical guage at the oil pressure port to test your guage?
What is you oil pressure? Cold? Hot? How many RPM's?
When you installed your pump did it have a gasket? Did you install a new gasket? Is that gasket directional and is it on upside down?
Wow,I sound like a drill instructor, but these are things I have seen in the last 35 years of being an auto tech.

I didn't do it, no one saw me do it, you can't prove anything! "Bart Simpson"