hmmm, my aunt had a cylinder miss fire a week or so back. she replaced the plug wires and the coil and it solved the problem. i dont know your exact truck type, but try changing the spark plug wires and the coil (if you dont have a coil, replace the distributor.) see if that works. the price may run you around $100. im not promising it will solve the problem, im just sayin what i know from past experience.
best of luck and pray its not mechanical