I have a 2001 F150 with 4.2L and about 104K miles. At about 90K, I got a misfire on cylinder 3 (P303) and I replaced the coil. I replaced it with an Autozone brand (Duralast). About 8 weeks ago,I had the same problem and replaced the plugs, wires and coil. The engine ran strong again. Yesterday, it started running rough again, the CEL came on and it threw P303, P304 which are the misfires. I called Autozone and compalined about the coil failing in 8 weeks. They replaced the coil for me free of charge and I changed it out again. It is running fine again.

Is it possible the coils (Duralast) are just junk, or could there be something about the truck causing them to fail?

 

Duralast coils are junk. So are their plug wires.

 

I've replaced two coils so far. 1st was stock at approximately 4 years old. It had a visible crack in the bottom. 2nd was aftermarket (Visteon), it also lasted 4 years and then cracked in the botom. I'm back to Motorcraft now but only because it was cheaper than aftermarket. The telltale sign of a cracked coil is missfiring and running crappy only after sitting overnight and goes away once warmed up.

 

It could be that the Duralast brand is crap. But something else is how sensitive these trucks could be to electronic/ ignition aftermarket parts. My '99 5.4L doesn't like any other type spark plug but the motorcraft, or it would run like crap. Don't have to buy from the dealership to get the Motorcraft parts which is good if you don't like spending $10 for 4 spark plugs,like me!