Yeah I was wondering if the pump used to test was leaking. Seems like if the FPR was leaking that slowly, it should still be pretty near if not functional enough to run the engine, especially on a design with the fuel return where it's pumping more fuel than needed and only has to reach 30-ish PSI.
*I could be wrong* but the fuel pressure test should tell you, and I assume when you replaced the pump that you replaced the fuel filter too. If you didn't then I'd replace the filter before pulling the tank down IF your pressure is low.
Am I recalling correctly that the FPR that uses has gotten really hard to find? Thought I read about that a year or two ago in a topic here, or maybe it was just for my '98? Don't recall when the FRP changed from year to year, thought there were at least a couple years of Explorers affected. [Edit]Yeah the SOHC was only in '97 and '98 with the return fuel system so it looks like only those two years have the different FPR? [/Edit]
When I lookup FRP for your '97, or my '98 4.0L SOHC on Rock Auto, they only show the sending units in error, were only for '99 and newer which had the FPR on the sending unit.