Spark plugs and knock

[billcar9999]

I have subtle problem I need help with. The truck is a 2001HD 8.1CC 4x4. The truck has about 48K miles on it now. The truck always had a flat spot in acceleration. I attributed that to the air box. I replaced that with a K&N then a Volant. Performance improved and the flat spot went away. Around 35K it started to bog when accelerating from about 45 up to 60. I'd have to kick it to get it moving. Around 38K I put in a Westers PCM and performance improved for a couple thousand miles and the problem came back. Then I replaced the plugs (Iridium) and wires. They definitely needed it. I didn't really give them much thought before because they were 100K plugs. They looked a bit like the plug at this link

 

http://www.centuryperformance.com/images/tech/Plgdetn1.jpg

 

except the insulator was still intact. However, the insulator was very discolored in the same shape as the broken insulator in the picture. My plugs did not have pitting/splatter that this plug has but were definitely worn. I checked the new plugs a few thousand miles later and I have the same discoloration. I haven't ever had a pinging problem. I did a carbon treatment on it with no real improvement.

 

Now my combined mileage has dropped off to about 9 (from 11-12). My highway mileage tanked to 10 (from about 14). I still have the bogging problem. I did switch to 93 octane fuel a couple of tanks ago. Performance is better, more power, etc but the mileage still is around 9. Air filter is good and the fuel filter was changed around 25K. I do have a slight miss at idle.

 

I'm leaning towards a marginal knock sensor. What do you guys think?

 

Sorry for the length.

 

Bill