Fuel pump. Welcome to the site, I'm betting your fuel pump has checked out.
Grab an EFI system pressure tester kit from your local auto parts store tool rental, T it into the outlet line from the pump, the one heading to the injectors, and see what your system pressure is doing. It should hold steady at ~51psi. If it's not up to snuff, check out Quantum's kit. Lifetime warranty, ~$100 bucks, can't beat it.