Man I just got done fixing this exact problem on My 99 and my Mom's 95. I did like you and replaced the plugs and valve cover gasket set only and it was fine then started all the stuttering again. Then I removed my plugs, cleaned them and installed new replacement wires. Problem solved. Since plugs aren't expensive, I would say get a new set and gap them. Install the new wires you have and all will be well. I bet.