My 2004 started shuddering at 45mph or while going up a 4-6 degree hill.
It was well past the suggested 100,000 mile spark plug change. I thought about changing the plugs myself until I heard that they could possibly break and would be difficult to remove.
I took the truck to a shop and had the plugs changed.
For about 2 days it ran okay, but the shudder returned and we got PO303 (mis-fire cylinder #3), PO316 (mis-fire on start-up), and PO171 (system to lean, bank one) Codes. The shop replaced the fuel injector on cylinder #3 and again the truck ran okay for about 2 days.
My son and I cleaned the other three injectors on bank one, cleaned most of the sensors and the MAF.
That work cleared the PO171 Code, but we still had a mis-fire on cylinder #3.
We swapped the spark plugs between #1 and #3 and got a mis-fire on cylinder #1.
We replaced the plug on cylinder #1 and that cleared the code.
The truck is running great.

 

welcome to the site. Sounds like you finally got it worked out. What replacement plugs did the shop use? Motorcraft or champion? it sounds like that plug was bad.

 

They used Autolite plugs.
The removed plug, which was new, had begun to come apart at the point below the threads.
Thanks bigunit54 ... happy to be a part of the forum.
Hope my post helps other enthusiasts.

 

Motorcraft plugs only!! SP515 are only $7.00 each. Autolites have proven time and time again not to work.

 

Thanks for your reply.
I will use Motorcraft when I change the plugs, again, which will be at approximately 40k and not at the recommended 80K miles.
I will also use the 1 part plugs, which I did not use this time due to cost quote from 3 or 4 sources ... $22 - $30 per plug vs $10 per plug.