Another option would be to replace the gauge on the pump and see what happens.
Mechanical gauges are most accurate at the center of travel. The larger the sweep angle the better the accuracy. 1" gauges are by nature inherently inaccurate as the swept area is a very small angle. The best solution for a small gauge is to use a 5 or 6K PSI gauge on a 3K fill gun which places the needle directly in the middle at full fill.