Spark plugs!
 

I know these engines are very sensitive to ignition conditions, but damn I didn't realize how sensitive!

Changed my spark plugs yesterday, with the latest and greatest Motorcraft plugs, didn't break a single one; the old plugs had 50-60k on them, truck currently has 152k. Truck ran fine, smooth, with decent power and no misfires before, such that no one would every notice anything, but I was amazed at the difference after changing them! The difference in power is night and day, even with the old plugs being within normal lifespan of plugs. The gap on the old ones was noticeably larger than the new ones, and they came out dry. A couple felt too stiff coming out, so a gentle soak with TB cleaner was used while I moved on to other ones. Also took the opportunity to thoroughly clean the boots, and apply new dielectric grease. Only on one other vehicle (my '84 GMC) have I ever come across a vehicle to respond so positively to new spark plugs.

Wife doesn't fully appreciate the task of plugs on a 5.4 3v (most whoever never done the job actually do, I know I still don't), but wanted to share the results here. Moving forward, they are definitely on the 50k mile replacement plan.

Yeah...
The 5.4 is very picky

With 154K miles... I would of replaced boots and springs.

Already did, a year ago. Replaced all 8 COPs, actually.

Good deal... what brand COP's did you install ?

I went with Autozone's COPs... not as good as the Motorcrafts obviously, but with their lifetime warranty, I'll never need to buy another one. Won't even need to buy a boot or spring, just exchange the entire COP. 3 had already been replaced before I bought the truck, so it's not like a tossed away a full set of Motorcrafts. I don't like doing things piecemeal, so when something like 1 coil goes, they all get replaced. I didn't know the boots/springs were designed to be replaced separately, possibly all she needed. Oh well, live and learn. Slowly working my way through all the little things with this truck... it was maintained well, but maintained in the way you'd maintain an old school vehicle, one not as sensitive. Changed all of its new brake pads with different pads because I didn't like the feel, etc. Full timing job in December...

Hey OP I'm at 142k in my 2005 5.4L, I just replaced all COP's with the autozone's just like yourself, but my plugs were replaced around 40K miles ago, currently I have a very rough idle and misfire uphill and in the 40-55 mph range. Even with the life left on my plugs, should I replace them as well? Your situation seems pretty close to mine.
Thank you for any help or suggestions you have for me!

I would install a fresh set of SP546's.. any DTC's ?