Did you check for any ECU codes?
What preceded this issue, a performance issue, hard starting, etc?
Full tank of fuel, change the fuel filter..? You mentioned a new fuel pump, was this installed before or after the fuel pressure read as low, fuel pumps designed for constant voltage (return style) & run always at 100% power may overheat in a variable DC control application (returnless). Verify it’s part #.
Little confused as to “cycling the key to reach 40lbs of pressure”, you’re just measuring the Prime? Check your Fuel pressure regulator for leaks & compare pressures after disconnecting.
Does the car run, what’s the fuel pressure read when the engine’s running? I’m assuming you’re reading fuel pressure from a gauge on the rail, what does a scan-tool read the fuel pressure as, may simply be a faulty gauge(?)
If the pump is running intermittent, it may cause low pressure readings, check your grounds, pump wiring. Less likely but possible, an injector or injectors that are stuck open.
Have a shop manual on the vehicle?