2003 Montero Sport sputters after the engine gets warm. on 2003 Mitsubishi Montero Sport

Our 2003 Montero Sport sputters once the engine gets warm and will continue to do this every couple of minutes, its as if you are running over the rumble strips on the side of the highway. We have changed the catalytic convertors and also put new plugs and wires on the vehicle but it didn't get rid of the problem. Wanted to know if someone had a better clue on what to possibly check. This things were changed after the vehicle went to the dealer and was checked by their computer. Could this possibly be the mass air flow sensor, or the O2 sensor?

Asked by for the 2003 Mitsubishi Montero Sport