Search hasn't turned up anything useful so far, and I'm not really sure what I'm experiencing to help me search. I'm getting an occasional shudder just like I'm riding over low train tracks for about 10-15 seconds, then it goes away briefly. I'll get a significant loss of power, and serious jerking. If I could describe the jerking, it's sharp like the truck is chain driven and the chain is slipping on the sprocket. Sometimes I'll get just a single jerk, like a gentle pop.

This can occur at speeds between 35-50, low rpms or high rpms. It's just not predictable. Sometimes I can ride the entire way to work and it won't happen at all. I just took a 5 hour trip at 70mph and it never happened but today on the way home from work I didn't think I'd make it back. It starts and idles perfectly, I also cannot make this happen sitting still in the driveway.

My initial reaction is something transmission related? Can the trans or lockup converter do this? I get it in any gear and with or without overdrive.

Can a loss of vacuum do this? I haven't seen any bad vacuum lines so far.

Could this be spark related? It would have to be killing multiple cylinders at a time for the shaking to be this bad. Spark plugs, wires, cap and rotor have 5 years and 20k miles on them. What about the coil? I've read something about a PIP but I don't know what that is. Would a bad PIP do it?

ANY direction would help at this point. I'm at a loss. 90% of the time the truck runs like it's brand spanking new. It turned 100k miles this week.

 

I found a video showing what I believe is my problem. This guy says replace the ignition coil. I'll try that this afternoon and see what happens. The ignition coil is original to the truck so it's probably time to replace it anyway.

 

UPDATE

Ignition coil did not help because the problem was the torque converter had all but exploded. Bits of it were laying in the transmission. I put in a new torque converter and the problem was still there, so I knew something in the engine was destroying the torque converter.

My fuel pressure was good, all plugs were getting spark, all sensors were working and got no codes. I started researching TSBs and found one from 1993 about the fuel injectors in early fuel injected 5.8s were prone to clogging. After 93 or so, Ford used non-clogging fuel injectors.

I disconnected the fuel lines and ran a quality fuel injector cleaning solution mixed with fuel pressurized by my air compressor through the system and let the truck run on just cleaner for a few minutes. After doing this twice my truck runs like it's brand new. Anyone with older fuel injection systems, I recommend getting on a fuel injector cleaning regimen soon. These things will be expensive to replace and they are impossible to test without pulling them out. That's a lot of work when cleaning all along may help prevent this situation.