5.7l

I have a 1998 GMC K1500 Z71 offroad with the Vortec 5.7L 350ci V8. Cold air intake True dual exhaust (no cats, dual in/single out Magnaflow muffler) Nothing else done to the engine this far. Idle is 600RPM, my oil pressure fluxuates from nearly 0 at idle and back to normal at WOT. Not sure...