If the truck is running then you have oil pressure.
If oil pump is shot then it won't provide oil to the HPOP.
If you're going off the stock gauge then that is just a dummy gauge. Shows good oil pressure at a set value and that's it. May be 10psi or so when it shows "good." @Patrick Feeley probably knows the details.
I'd suggest replacing that switch/sensor and see what it does from there.
It's 6 or 7psi for the factory switch. If you disconnect and ground the switch wire, it should show about midscale on the gauge. If it doesn't the wiring or gauge could be bad. You can test the switch by checking to see if the switch has continuity with ground when the engine is running. It should and if it doesn't the switch is bad. Cheers!
A forum community dedicated to Ford F-series owners and enthusiasts with a Power Stroke diesel engine. Come join the discussion about performance, bulletproofing, modifications, classifieds, troubleshooting, maintenance, and more!