if you think you have a misfire you should take it to a shop and find out what cylinder is misfiring. If they have a scanner they could see which cylinder is misfiring. If they have a scope they can see which cylinder and also see what the spark is doing. They could see if the spark kv is too high, bad plug or wire. Too low, flooding or low compression. They could see if the cylinder is running to lean by the burn time and slope or rise Once you find out which cylinder is the problem then you can concentrate you efforts on that/those cylinders.
'replacing everything' doesn't help me understand what your actual problem is and what you have done to it. what things have you replaced? Does it miss all the time? Worse at times? Missing at idle? Does if feel like it's just one cylinder that's missing or is it more than one? have you checked your fuel injectors? Have you checked exhaust back pressure? Have you checked for a vacuum leak? Checked your EGR valve? Did you do a compression check?
is it a light miss so that the engine shakes or is a hard miss that shakes the whole truck when driving?
the most important thing to diagnosing something that isn't right in front of me, is information. If I had the vehicle right in front of me, I would be able to see and hear the engine run. I might even test drive it to feel how it runs under a load. I would scan for cylinder misfires. Look at the fuel trims and the O2 sensors. I would put it on the scope and look at the firing pattern of the cylinders. But WITHOUT all of that I need as much information as you can give me to try and give you a direction to go in.
If you do have a particular cylinder that is misfiring you could pull individual spark wires off the distributor one at a time and then put them back on, to see which cylinder isn't hitting good. Then you could concentrate on that cylinder.
Good spark, fuel and compression are needed. Compression could be low from rings or a valve problem. Spark could be a plug, wire, cap, rotor or the distributor. Fuel could be fuel pressure, injector, vacuum leak or problem with the intake valve.