oil pressure sending unit could be going bad but the vehicle at idle should be producing a minimum of 4 psi of pressure at the sending unit at idle (MINIMUM) and should go up from there. some times under load it may see less than normal at given rpms. oil pressure is developed inside the engine not at the pump . so if oil pressure is dropping it could be internal failure of parts.
Working on a 08 uplander that intermittently losing oil pressure (light on dash) driver let it go and now BAM!!!!! catastrophic misfiring under load and horrible noises. going to be digging into the engine on monday