I aint big on the OBS trucks but I know on mine that the gauge is not really a gauge, it is an idiot light with a sensor set at around 9 psi. If yours is the same then it could be that below 1000 rpm it falls to like 7 psi and above 1000 the pressure rises to above 10 psi which would cause the gauge to spike back and forth. I believe I’d put a mechanical gauge on it and test it then, if it is real and not a sensor issue then I’ll be praying for you.
I have a real gauge on mine that I added to my overhead gauge pod. With my old motor I idled around 20 psi and ran around 40 cruising and up to 70 floored. New engine idles around 50 psi and cruises around 75 and pegs at 100 floored. My gauge is a cheapo so it may not be exactly accurate but you get the picture.
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