Have you verified the oil pressure with a manual gauge? Takes just seconds to install and you will know... I dont get into the snake oil treatment arguments.. cheap junk for me..
Cause these engines are tough and if everything is right inside it, no need in fancy oil

 

I don't know how anyone can claim the bearings suck. I have 200k on my '00 4.0 and its just a baby compared to some.

 

20w is how thick the oil is when cold. The oil is thinner when cold to aid in cold staring during the winter. Because it's thinner it's gonna flow through the pump and sensor faster giving you a higher pressure reading. As engine warms the oil goes to from the 10w to the 50 meaning it thickened. Thicker oil will flow slower giving you a lower pressure reading but it provides the most protection/seal. Also as RPM rise pressure should too.

With that said, and from what I recall,
Chrysler got sick of people being concerned about pressure fluctuations so they made a updated oil pressure switch that doesn't fluctuate and stays fairly stable unless something is seriously wrong. So to "fix" the problem you could just get one of the dummy pressure switch.

 

That is not how oil viscosity works.

 

I would address this issue with some urgency. Like Blackbox mentioned, verify that the actual oil pressure in oil gallery is within limits. It is highly likely that the pressure sender is giving a false reading. If the actual pressure is low and giving cause for concern, then it can be a few things. First check that the strainer/pick up to the pump is clear. If it is the take off a big end cap and measure the clearance with Plastigauge. The tolerance's are in the manual. Do the same with the main bearings and again check the tolerance. If you find the limits have been exceeded, then it is time to think about your next course of action. If it was me, I would remove the crankshaft, check for ovality and wear, re grind if necessary and replace the bearing shells with new standard or undersized ones. Unfortunately if the bearings are worn, no amount of thick oil will solve the problem. The I6 engine is very straight forward to work on, but like any other engine requires the bearings to be tight I order for the correct oil pressure to be achieved. You might consider replacing the piston rings while you about it, that way the engine will be in good shape for many years to come. The good thing is the parts are cheap and readily available. Using OEM parts is usually the best way to go, especially with Pistons and shells. Keep us posted with progress.

 

Also dont listen to that MEECHHHH.... He super chill cause he spending YOUR money..

The bearings in these tractor engines are stupid strong... Put up with water in oil, gas in oil and forget to change for 20k .....

300k is easy to do with just normal 5-7k oil changes... we had a fleet of cherokees.. 250k was minimum miles on them before we switched out to silverados, and we idled those jeeps 1000's of hours while on duty.. I bought mine and drove it another 150k... still good when I sold it to a hunting camp.. Still up at the camp hauling everything and only getting gas in return.

 

If you are having erratic readings and there are no mechanical or drivability issues, it's simply more likely a failing oil pressure sending unit. Oil pressure at idle per FSM is only 13psi. It hovers around 40-60 psi when driving.

As Blackbox has posted, check the pressure with a mechanical guage.