good deal man
i don't know how many times i've ran across that on these cat trucks.
i finally got to the point when i found misfiring happening the cap was the first place i looked and 99% of the time there were cracks there causing it.
just doing a simple tune up of new cap, rotor, plugs usually fixes it and if need be new wires too if the old ones are cracked or the boots are damaged.
Glad i could help out
Have a great day and be safe :)