Oil pressure gauge issues
 

I am having some issues with my oil pressure gauge. I installed a 350 crate engine with a new under hood wiring harness. the sender was new as well. The gauge worked fine for the first couple months. Now it sometimes will go up to around 30 psi at cruising speeds, but typically stays around 15 psi max. With the engine off the gauge goes and sits right at 0 and once I start it it will jump to 15 and stay there. I have replaced the sender with a new delco unit, replaced the gauge itself and also checked all of the wiring and connections AFTER I hooked up a mechanical gauge to just make sure I was getting the wrong readings. I had 25 psi at idle and 45-50 at cruising speeds.Could this be an issue with the circuit board on the gauge housing? Anyone ever have this issue before? HELP, I want my factory gauge to work like it should.