I would get or rent a fuel pressure gauge, so you can either find out if that's the problem or move on to something else.
Fuel pressure should be 30-45psi, during the test run engine at 2,000rpms for at least 1 minute to see if pressure is holding.
Fuel pressure is set by the Fuel Pressure regulator(FPR) on the fuel rail, it has a vacuum line attached, and 2 fuel lines, IN from filter/pump and OUT-return to fuel tank.
It has a spring to hold the OUT passage closed when engine is off(fuel pump has a check valve to prevent fuel from drain back into the tank).
When you start the engine and it is idling the Vacuum in the intake is highest, so FPR vacuum line pulls open the spring valve and extra fuel flows back into the fuel tank.
As engine RPMs increase the Vacuum drops and spring valve closes.
Remove this vacuum line and check it for fuel or fuel smell, if there is fuel then FPR rubber diaphragm is leaking, replace FPR.
Plug the vacuum line with a screw or bolt, so no vacuum leak, start engine, make sure no fuel is leaking from vacuum port on FPR.
Fuel pressure should be 45psi or higher, if not then FPR is not closing OUT valve all the way, replace FPR.