I had this issue in my civic and after I put a bottle of fuel system cleaner through, it went away almost instantly. The car would randomly misfire up hills because my fuel pump, lines and injectors had crud in it. The chemical treatment worked perfectly and I never had the problem again ever since I started adding the cleaner once every oil change. Sounds like it might be fuel system or air flow related. Is your air filter clean? If none of those things, perhaps fuel pump or fuel filter related?