Truck misfires when I accelerate, most pronounced at higher speeds. I have replaced the fuel filter, replaced plugs and wires. Still no change. What's next? Oh yes...no engine check light has gone on. One other issue. Soon after the engine warms up, my water temp. gauge needle quickly flashes hot for about 10-15 seconds, then goes back to the normal reading and remains there. This has happened repeatedly the lasr few weeks. Thermostat change?