Has been awhile since I replyed to this thread. The eBay coil packs are still going strong and I've put about 20K miles on them since I installed them. I still say they are the best deal going but you non-believers keep throwing your money away at the Ford dealer. I still think these are factory VISTEON packs. Can't prove it but I'm a happy camper.
I talked to a engine dyno pro about the coil packs. He is using the stock ford 5.4L truck coils to make 800+ HP in a Mustang. Like stated above they work or dont work they dont wear out or get weaker with time. Replace them only if they break and don't waste money on the advertised hotter coils. they won't get anything extra and could burn the piston if you run lean.
I just installed a set off ebay using the "How to replace your 4.6L & 5.4L spark plugs" thread to guide me. Total cost was around $120 for eight shipped.
Supposedly the truck wasn't throwing any codes but OBD at the dealer said two were starting to miss. It was noticible at cold start up idle.
Install wasn't too bad. It took me about 1.5 hours at most with the above thread helping. A quick run in the truck and I can tell an immediate difference in idle. Felt like the truck wasn't running. I like that.