To axlehead;
Take a good look under the truck for any signs of dirt collection leakage that may stream along the underside from the airflow and not drop off when setting.
Gaskets that seep will do this and cause loss of oil level over time more then you would think.
The PCV valve can add to it, the intake valve seals, a dip stick tube that has rusted through.
My experience now with 194+ k miles has been an oil level ups and down over the years and caused me to wonder as well.
Last oil change I changed to DEFY 'Blend' 5W30 as sort of an experiment.
This oil has a seal conditioner added that is not in Motorcraft oils as far as I can determine.
The results are less loss in oil over even a longer change period and an average increase in oil pressure of about 8 psi.
The cold pressure will be very much higher before the oil heats to normal temps.
Just changed again now with DEFY 5w20 to see what the difference might be.
I expect lower oil pressure as it was before the change but want to see what the loss is. If still lower then I can attribute it to the seal conditioner in this brand oil.
Good luck.

 

Bluegrass, as with any high mileage oil it will come with seal conditioners at a level not found in conventional oils. All oils have them, just at what value. I would expect the 5w-20 to yield a lower oil pressure especially with your mileage and a thinner oil. I would suggest if you decide to experiment a little more to use the 10w-30 Defy. Be aware that the CCS rating on it is only 6400@-30F which means even though it's a 10w oil, cold startup is not an issue. The 10w-30 has significantly more ZDDP than the other viscosities they bottle- usually in the 1200-1300 ppms range. Otherwise their claims to have more wear agents falls to advertising hype with the 5w-20 actually being a SN rated oil by formulation whereas the 10w-30 is really an SL API rated oil. For folks that have the older flat tappet engines, here's an alternative oil for your vintage engines. The only issue I see with the oil is the posted NOACK rating at 12%. That's pretty high. NOACK is the oils ability to evaporate. I have no real world data to tell you if that's actual or just a number to get the white paper out on it. The Viscosity Index is 152 which is the same as MC oils. The HT/HS rating is 2.67 which means it barely makes grade but HT/HS rating is not near as important as it once was as the formulators are using film strengths versus viscosity to keep parts from touching. Any engine can and will benefit from moving up in the viscosity range when it has lots of miles on the clock. I'd suggest staying with the xw-30 oils for your engine.

 

Thanks Labnerd.
Good info.
At nearly 195k with a near perfect running engine, the MC oils are almost 75% higher in cost from what they used to be and my source was out so decided to try the DEFY blend at less cost.
I liked the result 'from the outside'.
Goes to show that one can't always rely on the label and much of what they give on the labels.
What attracted me was the claimed extra Zinc, the blend, the stated seal/gasket conditioner and the cost.
I appears it's a good alternate oil to consider.
Good luck.