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Have you tested the fuel pressure yet? I would start by doing that If the fuel pressure is not right in spec than you could have a failing pump or bad connection at the wires. Check the fuel pressure as it is a common problem on this vehicle. Since this is a mechanical returnless fuel system (there is no fuel return from the engine to the tank, and the fuel pressure regulator is part of the fuel pump assembly in the tank), if the pulse damper is not leaking and there are no external leaks, there are only 2 possible causes of rapid fuel pressure leakdown. One would be leaking injector(s) and the other would be an internal failure in the fuel pump. If an injector or injectors are leaking, normally there will be signs of a rich, or "loaded up" condition when the vehicle is started, such as a puff of black smoke out the tailpipe. To be sure that the fuel pump is the problem however, remove the fuel line from the fuel rail and install the fuel pressure gauge into the line. Then, cycle the key to build fuel pressure, and if it still leaks down when the fuel pump shuts off, replace the fuel pump. Be sure to replace the whole fuel pump assembly, as the check valve and pressure regulator are part of the assembly.