2004 2500 HD 4x4 low oil pressure

04 2500 HD 4x4 6.0, A few days ago I started it up and noticed I had maybe 5psi oil pressure, killed it checked oil level and good, searched online for a bit and started it up again and same thing but no engine noise at all, no knock or tics. I drove it down the road a little and within a minute the pressure came up to 50 when pulled onto pavement and accellerated so I drove easy to store and pressure stayed up the 10 min drive. At store killed it and when leaving and started it, 5psi again. Turned and accellerated a little and it came up and stayed 45 to 55 entire time driving home. Killed it and immediately started it and 5psi so I shut it off and did lots of reading that night. Different stories of bad pickup tube o rings and screens clogged and oil pump wore out or sensors. So I just got a new oil pump and pickup assembly, o rings and all so I would have it ready. I know this is a common problem, my concern is I have a 4x4 wich makes dropping oil pan more complicated than should be. If I get that far in to it Ill change it all, but any insight into job or advice or what I might can check first that will lead me to a plan of action I would greatly appreciate it. If I dont have to go as far as dropping the front diff and front end alignment after and all that at this moment, I wont. But if I have to then I will. I am trying to come up with a good process of elimination bc if I really have to get that much into it, I would rather get some more parts and replace them too while in there, right?

Easier and cheaper to replace the OPSU (Oil Pressure Sending Unit) 1st. They go thru many heat cycles and become brittle and wear out. I'd swap in a new one 1st before going in the oil pump.

Now if you still have the issue.

1 - get you a new timing chain. If you've been running the stock one since 04 you're more then likely so over due to replace it. You have to remove the front cover to get to the oil pump, you have to remove the timing chain, might as well replace it.

2 - More than likely you're going to need to lift the engine off the mounts a couple of inches to make room to clearance the oil pan to remove the pump. Pay attention as you raise the motor to make sure you don't crush anything. I would use one of those cross bars that can hold the engine up like they use for removing the k member or front wheel drive cars. IMHO it may be easier to just pull the motor then go thru the hell of raising the engine, fighting the front diff, and all the other BS in the way. If you just drop the pan, drain it then stuff some rags (count them) around the pick up tube to prevent anything dropping in the pan before you pull the pump.

3 - make sure you have the correct o ring. Oil Pumps sometimes come with multiple o rings.

Thanks for the advice, that is a good point. I was thinking if I had to go that far in it, it would be silly to just put in a pump. I have been busy with other stuff but after I change the sending unit I will let ya know how it went. Thanks