This never used to happen before. But now, when I'm idling, my oil pressure gauge says ~ 1.5 kg/cm2 and when I get up to 3k+ rpm, the oil pressure gauge moves quickly up to around 6 kg/cm2. Before it wouldn't move as much as it does now, it would just hang at ~ 3-4 kg/cm2.

Stumped.

 

Substitute a known good hand-held gauge in place of the sender unit, and compare the pressures with what the original gauge was doing...If the pressures aren't the same, look into the sender unit/wiring/gauge cluster, if they are the same, look into e-shaft thermal pellet/front cover o-ring/pressure regulator valve/oil filter...