This has been covered before, but I thought it worthwhile to share my experience...
I bought this truck, and the previous owner said he had just replaced the plugs 10k ago, among other things (re oiling the K&N, etc). He said not to bother doing em as he had bought "the most expensive plugs", which turned out to be the bosch 4 prong plats.
You would not believe the difficulties I was having with this truck. Poor gas mileage, hard starts, and finally no start. And why? Because I was running on MAX 5 cylinders, more likely 4.
When I finally pulled the plugs (after replacing my spider and nut kit to no avail) I couldn't believe the condition they were in. All of the plugs were covered in black sooty crap, and two of them had major *chunks* of carbon between the electrode and the prongs. These chunks had the thickness of a CD and were as wide around as a pea.
So when people here recommend you use nothing but AC delco rapid fires or plats, listen. Now that I have the rapid fires in my truck its running great.