It sounds like oil pressure sending units are an issue for these trucks… where is it located?
The oil pressure sending unit is next to the distrbutor and unfortunately under the overhang of the windshield. Remove the air cleaner, you will have to feel your way. I think you’ll need a 1 1/6" deep socket to replace it, buy the new one and check what size socket is needed.
Is yours leaking or not working?
I drove one for 135k miles without replacing the sender unit.