I have a 98 chevy cheyene 4.3 L with a miss on cylinder 6 can't fix it

When driving I get a miss at about 65mph.I usually get a check engine light. I have had it checked and it says a miss on cylinder 6.I have had the jets cleaned
and used shell v power gas and four gas treatments with stp.I don't get a check engine light now but still runs extremely rough beginning at 65mph and smooths out at 70mph but in between that time she feels like she is falling apart .Can you help me?
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On Fri, 01 May 2015 13:18:01 +0000, ivan

Have you checked the ignition? That can be the culprit.
Good information here http://www.aa1car.com/library/misfire.htm
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