First two cylinders stop firing together while driving

i was pulling away from the toll booth and 5 minutes later i could not climb the hill. i was decreasing in speed which it never did. so i stopped and the engine was rumbling as hell. i thought maybe a spark plaug failed out or a power pack but i persisted to finish what i had to do that day went to work on it today and cleaned the spark plugs since they are irridium and only 6 months old and changed the number 1 power pack cause how i checked to see if it was working was i pulled the the wire and still nothing. it was running so rough that i checked the number 2 as well and that was not firing either. so what would make to cylinders stop firing at the same time?