i want to change the plugs but i have heard some rumors about somethings happening with the heads after the plugs are taken out. also what is the best plug to run. my truck is not running to tip top shape, it just doesn't seem to have the power it should. the only thing have done is put a k&n air filter on it. sure doesn't feel like 300 hp to me right now

 

Some models of the 5.4L in the early 2000s had special two-piece plugs that proved quite problematic when maintenance came due....don't know if the '04 falls in that category.
In any case, the job is a bit daunting, particularly where #4 plug is concerned, so be ready for an interesting exercise in flexibility and patience.
The K&N filter may or may not have changed the flow through the MAF that is interfering with the fuel delivery strategy....could be wrong, but it deserves some attention.
I'd suggest putting the OEM filter back in place, then check for performance.

 

Check out the 04-08 section and you will get a ton more info. What it is is the 04s throuh 07s the plugs break off in the head. Check out Gatorb8s sticky at the top of the 04-08 section