I just changed out my spark plugs on my 87' GMC Jimmy. Once i started it up and noticed one cycle sounds like its mis firing alittle. It makes a little putt sounds every half a second. I gap them all at .045 which almost all GMC trucks are gapped at. I pulled out the old ones and they were gapped at .055. Once i heard the miss firing on one side of the engine. I pulled them all out and changed the new plugs to .055. i started the truck and still had the same problem.

What did i do wrong here???

Bad wire, cracked plug, switched a wire.

i bought all new wires and i know i didn't switch any of the wires, i might of over tighten one of the plugs, i'll buy a new one and change it out with everyone to see if i cracked one.