Who's running NGK ZFR5N in there Slant?

My story with Champion was, I installed new plugs, and the engine developed a misfire within a short time. After trouble shooting, swapped out the Champs for a set of used Autolites, and the miss went away. Swapped the Champs bck in, and the miss returned. I sent the plugs to champion,and got a response "there is nothing wrong with the plugs". They did not send a set of replacements, or even return the plugs I sent them.
By the same token, I had a issue with a set of Autolites. One plug in a set of 8 was 5 heat ranges higher then what was on the box. Informed Autolite, and they wee very apologetic. Offer to pay for any damage to my engine (there was none), and sent me a case of plugs, for my inconvience.