If you are using stock gauges, it *is* possible to get the wrong sender. Not sure which does what anymore, but the diesel trucks had different senders/gauges, because they had 80PSI gauges.
May not be your problem, but the wrong sender for the gauge will cause problems with the reading being inaccurate...it works, just the needle is in the wrong place. Example: A vehicle with a 60 PSI guage with a 60PSI sender, on an engine that puts out 30PSI, reads right in the middle of the gauge. If you put an 80PSI gauge in there without changing the sender, it too will be in the center, but read 40 instead of 30.
Soo, I guess if you had an 80PSI gauge with a 60PSI sender, indicated oil pressure would always show higher than actual.