We have had this happen to us at our shop. This is just the nature of the beast with this one. We performed a carbon depletion service on the engine 1st. This helps loosen the carbon up that is on the plugs. Then we told the owner to run 3-4 tanks of fuel with BG44K additive in the each tank. We told the owner to come back after he got done with the last tank of fuel that had the 44k in it. When he returned with the truck we were able to remove all but 1 plugs without breaking it. At that point you would need to follow the instruction of the other answer to this question.Make sure the engine is cold and use Quality tools and PB BLASTER to help lubricate the threads. If the plugs break there are some special tools that can be purchased from your local Snap-On tool dealer and I believe that KD Tools makes a removal system as well. Hope this helps.