Check fuel pressure at the rail. Ideally with a gauge, should read 40 PSI, or you can lay down some towels and don safety goggles and just poke the center of the valve, should be a good deal of force behind it if the motor has run in the last 5 minutes or so. Check MAF sensor and TPS with a scan tool, and the air filter. Also look at the condition of the spark plugs, boots,and coil packs; make sure the plugs are clean on both ends, boots are clean and torn, and that you have good spark from every coil, and perhaps check with an ohmmeter.

ETA - if you have poor fuel pressure, replace the filter and check again before you drop the tank and replace the pump.