I have pulled with a V8, a V10, a 5.9 C, and a 6.7 C, the one and only thing that helps with longevity and MPG is speed. I hand calculated for a solid month on each vehicle to find that sweet spot. I find at any speed, slowing down treats the motor better and ups your MPG's. In my 6.7C with an auto, I took an 8000 lb trailer to Cody Wy empty, loaded a 2.5 ton short bed with 5 ton running gear and 54's. I topped off in Cody, drove through Yellowstone to Bear lake, dropped the rig and hauled the empty trailer home on the tank I filled in Cody. Granted I only did 67 the whole way, but I did it. Oh, and my truck with a half tank hits about 9600 'ish with duals and a steel flatbed.