Some ?? about 318 build vs 360 build for my truck

Gas milage will be similar if they are properly tuned. Maybe 2-3mpg better with the 318 but I think the 318 will work harder and need more throttle. I've had /6, 318, 360, and 400 powered trucks. I like the longest stroke you can get. I'd take the 360 over the 400 any day.