1997 k2500 4X4 Misfire

Hi guys,
I have a 1997 Chevrolet k2500 4x4 with a vortec 350. It seems to have a noticeable snap in what sounds like the distributor at higher rpm levels.I pulled plug wires off and the number 6 plug wire that runs to distributor cap was corroded white. So I replaced with a used one I had laying around and it seemed to fix it, for awhile. Now it is doing it again.I switched wire around 2 months ago and it started missing about a week after. This is getting kind of frustrating!Any help would be very much appreciated. Thanks