Next would be to check the fuel pressure at the rail. Buy or rent a fuel pressure gauge and do some tests. Test it when ignition on to prime the pump and take note of psi reading. Should be 49-52 psi at prime. Then turn off ignition swith and watch for falling psi readings. If it falls to fast within 10 mins more than 10 psi, faulty regulator valve on top of fuel pump. Then try testing while the engine is at idle and running should see the same reading 49-52 psi, anything lower then this will shows problems. Mine was at 42 at ignition and when I started the engine would go to 37psi.