I have a 04 F-250 Superduty with a 5.4. I want to change plugs. I don't have anything apart yet, so I don't even know what I have. I think I have the HT plugs, and would like to have them in advance. I looked on the net, and no one seems to have these in stock or even give a price. Are they all the same or do they have different part numbers?