I have a technique that works every time with the factory removal pliers.
I turn the end until the metal is placed so that I can get the pliers on the metal, not on the rubber. Then I wiggle, if it does not come off, I get a big screw driver and place it between the pliers and the top of the cylinder head for leverage. Be gentle and work it and it will come off. Once off, I install some lube on the top of the plug.
1991 GMC Syclone
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