A friend of mine is looking at getting back into RV hauling, and wants some help on engine Choices. The email states a FL, but he will most likely go with a KW T270. See below... Here's what I sent them: Used Freightliner so I don't have to argue with doe heads about a Paccar PX6 and PX8 being a Cummins. Specing a medium duty truck for my RV trailer logistics company. Truck will likely be a Freightliner M2 with an Allison automatic transmission. It will weigh roughly 11,000 pounds and the biggest trailers I haul are between 12 to 14,000 pounds. I'm wondering, will the 6.7 (325 h.p./750 torque) be more fuel effecient than the 8.3 (at 1000 torque) or should I go with the bigger engine. I'm trying to run as efficiently as I can, but of all the RV and trucking forums I have posted on and dealers I have spoken to, I can't get a clear answer on this. I like that the 8.3 is a wet sleeve engine and more robust, but I don't want to give up fuel mileage. Thank You.