Failing plugs usually will misfire when under load only. Does it get worse as you hit a hill? Mine shook like crazy in O/D going up hills at 45-50 MPH and when I took it out of O/D to take low RPM load off of the engine, it cleared up right away. I can almost guarantee your issue is the same one I had. I replaced my spark plugs and it hasn't happened since. That was 44,000 miles ago.
One thing I want to mention; If you're not familiar with the spark plug design on these year 5.4s. These are not your regular spark plugs. They have a 2 piece design and the bottom piece of the plug is a porcelain shell that can break off in the head during removal due to carbon seizing it into the well. There is an extractor tool by Lisle part #65600 to extract the shell. There are some good videos on YouTube showing proper procedure for spark plug removal, shell extraction with the Lisle tool, etc. I also recommend running a few tanks of Chevron Techron before tackling this job, which will help to break loose the carbon from the porcelain shell.
Yep, plugs should clear you right up. I bet if you hooked up an obd reader and observed misfires, you'll see the counts increase as it shakes. Plug change out is a piece of cake just take your time and keep the beer cold and plentiful!
Would this throw a code? My is doing the same thing but doesn't show problem codes. I cleaned throttle body and MAF, changed fuel filter, cleaned air filter, etc. and it still shudders under acceleration.
__________________ 2005 F150 XLT SuperCab 5.4L V8 4x4, 3.73 LS Rear end, Auto Spring 2" Leveling Kit, Gryphon tuner, AEM Panel Air filter with GOTTS modified stock intake
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