Bad Oil Pressure Gauge

I am paying close attention to this and similar threads for any suggestions - still at a loss of what to do. Maybe replace oil pump as a last resort?
I have a similar issue with oil pressure dropping to 0 at hot idle and basically the same as everyone else. The 2 differences for me is I never have over 40 psi even at cold start and I never reach 210* until I'm on the highway - even driving around town for 20 minutes in summer.
Oil pressure hovers around 18-20 at 2k RPM which seems to be okay. I replaced the oil pressure sending unit with a MOPAR replacement but there's been no change. I will try resetting the PCM by disconnection battery but I'm always nervous when it comes to electricity.

Symptoms:
Cold start ~40 psi
Warm idle ~20 psi
Hot idle (eventually gets to 210 on gauge) drops to ~8psi then 0 and Check Guages light
Pressure will increase while I give it gas 1k RPM but drop as soon as I let off
Warm/Hot idle just below 500 RPM which seems a bit low?
2000 4.0 auto
 
After more research I'd like to ask you all, could it be my oil type and filter causing the low pressure?
My most recent oil change was with 5w30 and CarQuest filter, which is around the same time I started realizing the low pressure issue. I don't know what oil was used previously. Would going to 10w40 help bring back my pressure since my problem only happens when engine is warm?
I will definitely go MOPAR or Wix filter for the next oil change regardless of oil type.
 
Update from my 23 Aug post: all that I did before was not in vain, but after driving 100 miles my factory gauge dropped again and check engine light came back on. Same scenario, outside temp 95 degrees, driving home from work (30 minutes) up the mountain (10 minutes) with steady RPM at 2300-2500, pull into the driveway to park, then factory oil pressure gauge starts to drop. I was watching the aftermarket gauge it was at 10-11 psi. Next step I got a cheap oil pressure sending unit (BWD) to replace the new Mopar unit. Same results. Now for the good news and my fix. My Jeep has 168k so I replaced the oil pump (which was my thoughts all along just didn't want to do the labor) with a Mellings Oil Pump. This fixed my oil pressure problem. The old pickup screen was clean, cam and everything inside was clean. The old pump was wore out. I could spin it like a bicycle wheel and it rattled. The gears inside had to much play in them. I have excellent oil pressure now and the jeep has better response. Have driven it 200 miles and all is well. Next project: I'm researching cooling systems to get the temp down from 210. Planning on installing an oil cooler, changing out the mechanical fan with an electrical fan, replacing the radiator, switching to synthetic coolant, adding silicone hoses and changing the thermostat. Looking at Mishimoto products. $$$$$$ pricey but I guarantee it will run cooler. It was my failing oil pump that was causing the problem.
 
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Maybe I'm just stupid, but why would you want it to run cooler than what it was designed to run from the factory. All its operating systems are designed to run at optimum efficiently at 210 degrees.
Maybe I'm misunderstanding something.
 
Mainly because I live on a mountain and running cooler would help while at low speed off road, trail riding and rock crawling. When the engine oil get to hot it becomes less effective. I will also install a trans cooler, trans and oil temp aftermarket gauge.
 
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Update from me. I seem to be maintaining better pressure all around. Just completed a 4 hour road trip around 22 psi at highway speeds. Once the engine is hot I am still pretty low at 8-10 PSI at idle and only sometimes does it drop to 0 with Check Gauges light whereas before it would always drop to 0 at hot idle. A small improvement but I'll take it! I'm at 148k miles.

Changed oil/filter from Conventional 5w30 (brand unknown) and CarQuest filter to Castrol GTX 10w30 and PurolatorOne PL14670.

When I changed the oil I didn't notice any sizeable metal flakes but there was a little metallic sheen which is making me a little nervous. Still could be a worn oil pump or camshaft bearings as others have alluded to.
 
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