2000 Dodge Caravan Missing

I have a 2000 Dodge with a 3.0L engineand only 33,000 miles on it. The van runs rough and runs real rough at 45. The Check engine lite came on with a P0302 code which is a miss fire in cyl. 2. I change plugs, wires, cap, rotor and still had the problem. I took it to a mechanic and he did the same thing I did and it still misses. He said it looked like there was an arcking at the cap and wire that he could not resolve. He put some insulation around plug wire #2 and that seemed to help for about 2 months and it started again. I was upset and didn't want to spend any more money with him so I went to NAPA and bought new plugs, wires, cap etc. And installed them myself. When I pulled the plugs they all looked good except for #2 which was black. After replacing everything I went on a short trip (350 miles total) and the Check Engine lite can on again with a P0302 code. I pulled plug #2 and it was starting to show a black apearance again. Any idea what I should try next? If it is a new cap and wires do you have a brand that may be less likely to leak or arch? I am using Champion plugs because I've heard that using others will cause problems. Thanks for any help you may be able to give me. Sorry for the length but wanted you to have as much info as possible. Bama