Well, high cylinder temperatures can cause a misfire, so you should make sure your thermostat is opening and your coolant is fresh. Also if there is a lot of carbon build up on your valves they will absorb fuel and at high temperatures they will be extra hot and ignite the fuel before it's supposed to which makes that cylinder miss. You could try an air induction, or something else that would clean the carbon out of your engine.

 

it's fixed! well i finally got home at my normal time (no ot today), started truck and warmed it up, held throttle at 2500 for a min or so and it finally threw a code. well a few. i got a clutch enagagement code? then a random misifre and cylinder number 5 misfire. pulled number five, looked normal, but threw in a new one and bam it's alive! thanks to all that have helped and for getting me to keep trouble shooting instead of buying parts