I blame the carbon fouling/rich mixture on the EGR valve. When I bought the truck it was disconnected, and plugs were fine. I put a new EGR valve in it and it started fouling plugs. I also remembered I had the same problem with a 71 Charger with a 318 I had once. It had a EGR valve mounted on the manifold. I blocked it off and it stopped fouling plugs too.

 

I just replaced the lifters on my wife's car and it wouldn't run right and would barely start fule smoke everywhere and all plugs fouled. After reading this I realized the issue. I had the water pump out as it was leaking and I was waiting on the replacement the COOLANT TEMP SENSOR was still unplugged. You saved me a ton of work and money thanks 🙏