Engine misfiiring and hesitating

I have a 2001 Dodge Grand Caravan SE with 100,000 milles on it. Recently it has started to hesitae or misfire the odd time on the highway when I apply a little pressure to the accelerator to increase speed. Also I attempted to use the air conditioner and while still in park it starting hesitating, almost like it was running on 4-5 cylinders. One more thing, after a rain storm last week it also ran poorly until the engine had operated for 5 minutes or so. Could this be an ignition and wire problem?