03 F350 6.0L Lariat (stock) loss of oil pressure, still runs & starts
 

Hello everyone,
First post, have read hundreds.

So here's the skinny...
Truck starts and runs what I would call "good". After the truck warms up a bit (20-30 miles) the idiot gauge for oil pressure will bottom out (from normal to nothing right now, no needle jumping around) when at idle (traffic light/ stop sign). If I get on the gas the oil pressure comes back up to "normal" and will stay normal as long as I'm above idle. After this occurred I did an oil/filter change. Same thing is still going on. I also swapped out my 2 liquid batteries for 2 optima red top AGM batteries. I still need to replace alternator and voltage regulator, both are on the way out. Had tested batteries and alternator at Orielys cause I noticed the alternator was not registering at low rpms on my battery/alternator cig tester. I also had them put on a code reader on OBDII port. No codes popped up. I have not tested manually the oil pressure via air pressure test or adapting a manual gauge to the oil system yet. I do not have access to a good scan tool, although I see autoeginuity scan tool in the future, that card is just not in my hand at the moment. I have a new EOP switch but have not installed yet cause I'm leaning more towards my alternator and voltage regulator being the issue as they both drop at low/idle RPMs.

Haven't checked;
•Condition of IPR
•Condition of ICP
•Condition of Oil Pressure Valve
Although from looking at wire harnesses they seem pretty clean considering.

I also put a piece of plywood painted white under engine where I park to see if oil is leaking out. No oil on painted plywood.

Any suggestions, confirmations, would be greatly appreciated.
Any further info from me you guys/gals need to help solve just let me know.

Thanks,
First pick-up & first diesel owned, mechanically inclined, shade tree mechanic

Welcome!