The biggest issue is where and how far are you going to tow. A diesel is going to get better mpg under a large load IE: headwinds, steep hills, heavy towing. If you are on mainly rolling hills, light load, short trips either engine will be fine although gas engines are probably better at short trips. If you think that at anytime in the ownership life of the truck you are going to go to a heavy camper and tow heavy the Diesel in the right choice hands down. My older diesel gets pretty much the same mileage towing heavy or no trailer 13.5 on the highway at the speed limit and 12 in the mountains. I scale with just the truck and camper between 12,000 and 13,000 depending on how many toys are loaded on board. my horse trailer scales between 6-8000 depending on how many horses and hay is on board