Robot7600

So i recently bought a 1991 that one of the previous owner put upgraded oil cooler lines on. Since the previous owners possession the oil pressure guage has read 0 psi. I have since changed the oil pressure switch. Which made it go from always reading 0 psi to reading about 40-50 on a cold Start. And a little less than 30 driving around warm. But it never reads any more than about 25 psi or so after it warms up. Could the aftermarket cooler lines have something to do with that? Any ideas what could be the culprit of my issue?