I would definitely put a gauge on it to see what's going on. Or pull the drivers side valve cover and see if it's getting up there.
If it was sitting for a while and lost prime I would think you could easily hear the lifters clacking when running with no oil....
Verification that the idiot light is working properly is an important first step if you can't verify oil pressure some other way.
The sender/sensor usually fails shorted which is light ON, unless the connector falls or rots off then it won't work at all.