Could be a spark plug (there are two per cylinder - so could be one or both plugs). Could be an ignition wire. Could be a fuel injector issue. Could have an issue with the base engine or cylinder head - valves.
Start with the easy stuff - plugs/wires. Has the truck been tuned up lately? Once pulling the plugs, check to see if they are fouled or if they are clean. This could show signs of other issues.
I had the same problem and after $400.00 in repairs it came down to a CO2 exhaust sensor. There are only two of these sensors and when one goes out the truck runs like crap. Trust me stop and replace the exhaust sensor.
It's a heated exhaust gas oxygen sensor (or HEGO or O2, not a CO2, to clarify...)...
But that's not what's wrong with this truck. Oxygen sensors do not directly cause misfires. Under certain circumstances, they could cause the engine to ask for more and more fuel, causing an economy issue, but not a misfire.