How do i troubleshoot fuel problem for a 2000 Hyundai Elantra?

My 2000 Hyundai Elantra was starting but running rough. I replaced the mass airflow senser and the idole control valve, and it was running pretty good. I drove down the road 5 miles and it died and wouldnt start again. I added gas and started but died. I added more gas and its running, but rough again. could it be the fuel pump?