As far as a DTC, my transmission has a big slide in 3rd, like it sometimes never fully engages 3rd. The RPMs stay the same while road speed increases, until just before the 3>4 shift, then it catches the gear fully, RPMs and road speed climb together for a second or so, then goes to 4th. Now, there are ways the ECM PCM TCM (wtfe) could detect that and throw a code.. but it never does. Sliding clutches for an extended widow of time under load causes heat damaging the plates/bands and heating the fluid. This issue should set a code. But it does not. I'm sure their theory is, if it blows, hopefully it be outside of warranty when it does. They will not even fully acknowledge it officially when i brought it to the dealership for this concern.
point being, there can be problems present that the coded out of setting a DTC by increasing the acceptable slippage detection rate.
as far as the commercially available oil pressure gauge.. that's a fair point. we all know Ford's sensors are not particularly trustworthy historically.
I do replace the filter holder stem / drain port seal with every oil change so I have no reason to suspect that as a cause.
good input all around, thank you. (to all)