Caravan misfiring & running rough

Hi, I have a 98 Caravan with the 3.0 engine. I have been having a problem with the engine mis-firing. It is usually cylinder #1. I had taken it to a mechanic and he told me the valve stem seals were leaking and the extra oil in the cylinder and on the plug was causing the misfire. We put a extention on the plug to keep the tip away from the oil. It still misfired but it wasnt to bad.
Now Im having a problem with a intermittent problem of the engine running very rough especially when the engine is cold. When I start the van in the morning I have to keep my foot on the gas pedal or the engine will die. It does this for a couple minutes until the engine warms up. After it warms up every once in a while when Im accelerating from a stop the engine misfires so bad that the car wont go over 10 mph but smooths out after 10 seconds. If Im on the expressway it will be running smooth then all of a sudden it starts to hesitate intermittently. It gets much worse if the van is going up an incline and totally disappears when going down a incline.
The only code that comes up is the misfire on cylinder #1. Can some of the other sensors like the MAP sensor or Oxygen sensor go bad without setting off a trouble code? Also Ive seemed to notice the engine runs smoother after I disconnect the battery and reconnect it. I understand this resets the computer, but why would the car run smoother. It takes about 50-100 miles before the Check Engine light starts flashing again to signal the misfiring and the engine to start running rough again.
Does anyone have any ideas what could be causing the problem? It seems to be running way to rough for the problem to just be the valve stem leak. Thanks for any help you can offer.