Does overdrive gear cause low oil pressure?

When i drive in overdrive(4th gear) in my '95 camaro z28, the oil pressure is less than it would be if I was driving in drive(3rd gear). Is this common in overdrive or can their be a problem? The oil level is where it should be. In normal drive gear, oil pressure is about 40psi at 2000rpm driving at 45mph, but in overdrive it goes down to about 30-35psi at 1500rpm driving at 45mph.