Dead pedal or intermittent loss of power. You are driving down the road and you lose all response to your throttle pedal, typically while this is happening you are losing road speed. When the engine slows down enough, it senses where it is again and throttle action comes back. Or you have to restart the truck to gain back throttle function.
Hard start, long crank times, usually when cold but sometimes hot, runs for a few seconds after start and then clears up and runs smoothly, or engine sounds different or louder under load, or makes crackling sort of sound.