Do you know which cylinder?
Neat trick I heard of is to use a timing light to diagnose the wire.
(works better if you can do it in the mostly-dark)
Hook a timing light up to each plug wire in turn, and compare the flashes against a wall (or the side of the truck, or something . . . ). Missing cylinder should show up as a weaker/inconsistent flash, compared to the others, I think.
I've also heard of people spraying water mist over the plug wires while the truck runs in the dark, to reveal shorts in the plug wires.
If the timing light doesn't reveal the trouble, maybe Denny is correct, and it's not ignition-related.
don't know if I'm barking up the right tree, but hope it helps.
-Michael
