My jeep was doing it, it got worce and worce. I only have 40k on it to... I changed the pluges about 2 weeks ago and for the most part it stoped, I still have troble from idle to 2k rpm, but its 90% better, Im still trying to find the cause for the very low rpm spadering. I didnt see any spark jumping from the wires (when i was in a dark room with no lights on).
but it doset meen there not broke... sence your into the wires just change the pluges, $4 and its a cheep fix/test.