Just changed my spark plugs this past weekend in my '04 F150. It has only 48,760 miles on the clock but I thought I should change them out due to some of the horror stories I have read here.
I used the Motorcraft plugs and they were the same numbers that came out of the engine. The gaps on the old plugs were within spec, the color was a light tan on all but the front 2 plugs, drivers side. From what I can tell it seems that the 2 front left plugs might be discolored from excess fuel, judging by a color chart that I found online.
Going to run a treatment of Sea Foam through it next time I fill up. Possibly injectors dirty and not producing a good spray pattern.
The plugs came out very easily except the second from front cylinder, drivers side. When it became a bit loud and hard to turn, just ran it back in a couple of turns, and it came out good after that.
The new plugs had to be regapped. One had a gap of ~ .060 and the rest were ~ .050, I set them at .054.

I use my truck to mostly tow our 23FBS Wildwood Travel Trailer. Have not towed with it yet since the change, but it seems to have picked up some pep from the test drive that I have done. Figure that this use goes under 'severe duty' since I mostly tow with it and it is uphill any direction from home.

 

Do not use Sea Foam. Use the search button, and you will find many posts on the subject. Use a couple of bottles of Techron and you will have done it right.

 

I would recommend you use a torque wrench and torque the plugs to 28 ft/lb.

The horror stories are about the 5.4 3 valve, not the 4.6.

 

Use Techron for fuel treatment

and hopefully you'll do more research before doing any more maintenance on yer truck....

 

^^^

 

I usually always by name brand fuel such as Union 76 or Chevron since they have high detergent content added to their fuels. I don't burn cheap gas because in my experience it is not worth the few pennies or now dollars, that you think you are saving. Cheap grade fuels do not run right in my vehicles. Shell gasoline even does not run well. Mobil does but it is much more costly in my area than others.

I have used Sea Foam in other vehicles with very good results.

When I installed the new plugs, I used anti seize and torqued them to ~ 28 ft./lbs. using a beam type torque wrench.