This truck was running hot so I put a new radiator and thermostat in it. The Check engine light indicated that 2 and 6 was misfiring so I put new plugs and wires and new intake gaskets. The Check engine light went out. Drove it for 1 and 1/2 weeks and the light is back on saying 2 and 6 has misfire. What Could be going on now?Do you think when it was running hot that the head gasket needs to be replaced or could it be the valves?
You also need fuel and compression. A compression test will show if cylinders 2 and 6 are low. For suspected fuel problems, switch the injectors from those two cylinders with two of the other ones, erase the fault codes, then see if they set again for the same cylinders or the two you moved the suspect injectors to.
When discussing an engine-related problem, we need to know which engine you have. If it's a V-6, check if you have six individual ignition coils or a coil pack. With individual coils, switch two of them the same way as the injectors to see if the misfires move to different cylinders. If you have a coil pack and one of the coils fires those two cylinders, chances are that coil is failing intermittently. Ignition coils seem to be a common problem today, more than years ago.