Kind of uncommon symptom for these engines. The oil pump on the five and six cylinder diesel engines are chain driven. Your four cylinder engine has a shaft driven system with bevel gears in there.

I would not rush into an oil pump purchase quite yet. Not saying it is not the oil pump either. Just I might want to investigate it a little further first.

Also even though the oil pressure gauge is operated with engine oil pressure directly. (mechanical system) I would also want another direct reading from the oil pressure point on the engine.

Any major dents on the oil pan that might have gotten the oil pickup? Could even be too much sludge on the pickup screen. You did take off the pan and remove some sludge it seems. Did you clean the pickup screen and tube? I am not a working mechanic so take what I mention with a grain of salt.