Low Oil Pressure

I have a 2003 Dodge Durango SXT 4.7L V8. I had a seized engine and had a reman engine installed. After installation, my oil light came on. I had the oil pressure checked with a mechanical oil guage and found it to be around 6psi at idle at around 35-40psi at 3,000rpm. My mechanic suggested the oil pump that came with the reman engine may be defective, so I put a new oil pump in it. I also changed out the oil pressure sensor, and I am still having the same problem. The warranty company on the reman engine refuses to do anything because they say 6psi is a normal reading, however, it is apparently kicking the oil light on, so there is still a problem. Any ideas or suggestions? Thanks!