Ford guy here. I'd look for a nice 3/4 ton 2003 7.3l diesel if you can fine one. My 2003 was traded with a tick over 500,000 miles and only required routine maintenance. Unfortunately, the body fell apart around it. The new emissions standards are really hurting the economy of the newer diesels. I have a 6.4l now, and it's a totally different animal. Left stock, they are not daily drivers. They are designed for long, hard pulls on the highway. In that capacity, the 6.4's excel. Can't comment on the newer 6.7, it's out of my price range. The 2001 6.8 V10 I had made great power, and would pass anything but a gas station. Fuel economy in that rig was truly abysmal. I agree the cost difference between 3/4 ton and 1 ton isn't appreciable, and gets you stiffer springs in the rear.