The plugs are more than likely an Iridium plug, ACDELCO Part # 41101 with recommended replacement @ 100K. If they are original, you are pushing the limit @ 140K! If they were replaced, you should be fine with plugs. BTW, they should have a “bump” on the ground strap of the plug, so what you are seeing is normal. (See pic below)
Have you checked fuel pressure, or changed the fuel filter & air filter? If the wires are original, they should be changed using MSD, ACDelco, or Belden wires. The cheap wires will not work well with the high voltage DIS ignition system!