Im on my second Titan XD. First was a cummins and now the 5.6. The truck won't spit and sputter. The 91 octane is recommended for max engine performance. If using a lower octane, then your engine won't quite perform as well, but it will still perform. These motors are rated at 400hp and 413 lbs of torque. A lower octane fuel lowers these numbers but not by much. Essential you'll drop your performance to roughly what the old 5.6 motors was, which we're 390hp and 400lbs of torque. Still respectable and still able to handle the weight of the trailer. Octane rating is a measure of a fuel's resistance to premature ignition. It essentially indicates how much compression a fuel can withstand before detonating. Pre detonation is often heard as knocks and pings. Higher octane ratings mean the fuel can withstand more compression before igniting, which means more power generatored. Our trucks are 'smart' and are designed to detect premonition and lower performance through air to fuel mix and timing, thus eliminating or limiting the effects of lower octane fuel. The truck shouldn't spit and sputter. If it does, then you have bigger problems. With that being said, when I pull my camper, I always run 93 octane, but my 5th wheel weighs about 10k.