I'm hoping someone can help me troubleshoot an ongoing issue with my truck that has turned out to be a real baffling headache! I own a 98 F150 with the Triton 5.4L. She has just under 179k on er. But anyway, about a month and a half ago she just started chuggin outta the blue while going down the road! I was going about 30 mph when it started chugging and shaking on acceleration. The issue continued for week. The issue was present both during idle and while driving. She would chug and choke like she was about to shut down at any minute!
I took her in to have the codes read and was told cylinder 1 had a bad misfire, cylinder 3 also had a misfire. Other codes were lean mixture on both ends and my O2 sensor being bad. The O2 sensor had been bad since I bought her in 2010, so I focused on the plugs. I went in and replaced all 8 ( a real pain in the butt!). The coil pack on cylinder 4 was cracked so I replaced that too (I was taught if the packs aint cracked, leave em be). I put everything back together and she still spat and choked! So then I ran a bottle of sea foam through her on a full tank of gas; thinking maybe the injectors were dirty. She seemed to run a bit better, but within a week she was back to chuggin and chokin pretty bad.
My next step was to replace the fuel filter. Once again she started out running better (but not normal) and then progressively got worse again. I took her back in to have the codes read and NOW I was told cylinder 4 was misfiring horribly! THAT's the cylinder where I replaced the coil pack AND plug! So now last night, I figured the pack was defective so I took it out and back to O'Rileys and got the more expensive brand. I also read on here about someone havin moisture in their plug boots. So I tore her all apart again and replaced all the boots as well as the new coil pack. I reset the computer by lettin her sit for a half hour with the battery cable disconnected. Annnnnnnnnd...I fire her up and she STILL chugs and chokes. The only other idea I have is to clean the master intake. She acts like she is not getting enough of something...air or fuel. She no longer shakes like she did that first day. She also doesn't chug and sputter when idling anymore. But she chugs worse at lower speeds. On the highway she runs the best with just a slight inconsistent stutter above 50 mph. Any ideas? has anyone else had this issue?

 

Have a '97 Scab, 4.6 with 234,000 miles. My "chugging" was mostly a idle or low speeds. No one could find the trouble which started at about 180,000 miles.
Then last month the truck began losing power. Turns out it was all cat converters failing. New cats, it was a new truck.
I'm convinced the cats bring up all sorts of weird problems. I used Seafoam but no more. I don't if it helped cause troubles but???
My truck is an ex-California truck. I have FOUR cat converters.