On the towing, vehicle weight and tires size is a factor here too as is fuel octane. 87 is not a good choice for towing with a 5.3 (or any modern V8 really) as it will reduce performance because the ECM will here the knock before you do and retard spark (to limit consumer complaints) and with it power and MPG. The ONLY reason that the engine even has a knock sensor it to keep engine quiet when con