Oil pressure gauge

As the engine rpm's go up and down your oil pressure gauge will go up and down that is normal. Higher engine rpm's the higher the oil pressure builds.

If it is a real oil pressure gauge it should operate the way Saturntech stated. However, some manufacturers decided that they received too many complaints because the gauge actually operated that way so those added a resistor to the gauge which puts the needle at a mid rage position and it does not move.

Looking at the sensor and the wiring it appears that your truck has a real sensor so the gauge should move properly.