About four months ago I had a similar problem. I get up to around 45 - 55 mph and I would feel a sputter or jolt feeling.... When the first time I took it in, the mechanic pulled the plugs and noticed 6th plug white casing had somehow disappeared. They ran a test and showed the cylinder was working at a good percentage...whatever that means. However I am experiencing the same thing and am wondering if my engine is giving out on me (147472 mi). Please excuse the brief descriptions.

Do I need some kind of cylinder repair??

Do I need an engine overhaul??

I don't know what my options are, I would like to keep my truck.....
2002 1500 5.9L 4x4 - have replaced the transmission (143745 mi)