Sender is always a possibility, Prosport cheapie, but it seems to be acting right... Cold oil pressure shows bypass in the 75-80 psi range. Isn't that about right for the total range? Seems unlikely it would track pressure with RPM, be about right at cold oil temps, but then read extrordinarily low pressure at warm idle.
Filter was changed with the oil, doubt both were bad. If one let filter media go, then that should show up as restriction, right? That would be higher pressure.
I guess I'm just going to re-assemble tomorrow and hope for the best.