Moisture can get into the cap and wreak all kinds of havoc, your plug wire will also arc if there is a lot of moisture in the air if they are shot. A little test to try is to mist the wires with a spray bottle in the dark. You will see any arc'ing (sp?). I would do a tune up as Hydra stated.
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2000 Durango 5.9L SLT+ Flowmaster 40 "Custom" Ram Air 31" BFG AT T/A KO's Bilstein Shocks Hidden Hitch Sirius Satelite Radio E-fan conversion Smittybilt brushguard SSU's
This sounds similar to my problem....but as hydra had suggested there, I cleaned the tps plus new champ IR plugs, taylor 8mm wires, new cap and rotor.....it was also suggested to clean a tmp sensor...which I havnt.
Also a MSD blaster coil which I relocated from th front of the head and closer to the dist
Things were great for a week or so and it came back, so Im changing the tps and air temp sensor this weekend and will let you know the outcome