Aah Ha. After reading about "Waste Spark Ignition systems" on other forums I found out what is happening. Half of the plugs fire with reversed/bad polarity. These plugs firing with reversed polarity will tend to cause wear on the ground electrode. That is the main reason for the platinum tip on the ground electrode, to reduce wear on those plugs. For the other three, the platinum tip on the ground electrode is not really necessary. Thus, on my car, the 1,3,5 plugs looked really good. The 2,4,6 plugs were the worst. So, the obvious thing to do is to change the polarity of the plugs at 30k miles. On these engines it is very easy since there are three coils mounted at the front of the engine. Each coil has two plug wire sockets mounted right next to each other. I wonder if anyone does this? I read that on airplane motors they tend to rotate the plugs to extende the life of the very expensive plugs. Of course, you could do that on some cars, but it would be very difficult on our trucks.

Too bad, the 3.5 liter engines with the coil packs, this trick is not possible.