What would cause plug wires 1,3,&5 to burn in the same spots. No sign of arcing on engine. the plug wires are on the back of the engine.
Most likely there is a common heat source that they are too close too for the type of wires they are. I would recommend using a good set of Belden or Accel wires as a replacement set and if you can afford it get heat resistant, also use some Dielectric grease on the boots to aid in removal next time you change plugs but use sparingly.
Search Chevrolet Impala Questions
Chevrolet Impala Experts