Good suggestion trying a second gauge to insure accuracy, and I do have a second gauge and worth giving it a try. Its bran new in the box, just have to find it....
Main reason is I have seen many people here as well as other sites chase a problem only to find out it was a gauge accuracy issue. About the simplest and cheapest repair/test at this point. If the pressure is the same I would remove the pump and measure everything or just buy a new pump as they are cheap and easy to swap out. Heavier oil is just a band aid in my opinion.
