Plug wire arcing. Tried different wire, still there.
 

I replaced the engine in my 99 Blazer earlier this week, along with all new plugs. Started it up, and it ran great. Nice and quiet, and was very smooth. The next day, however it started getting a slight miss. I could hear it arcing, and found that it was at the #3 plug.

Since then I have tried 3 different wires, but the arcing is still there. A couple of times I thought it was ok at 1st, but after a moment it came back. Sometimes it's a slight miss, sometimes it's worse.

I pulled the plug tonight. The gap is set right, and there is no noticeable cracks or chips. Only thing I haven't tried is another plug. Will go to the local parts store and grad one tomorrow.

Any other ideas as to what it could be?