I have owned all of the Ford diesels, some for a while, some for short time.
2000 7.3 - Great engine, not super fast, but makes power in the lower RPM range and you can work on it without pulling the cab and nose. Some bothersone little issues, but very few. Great mileage, doesn't need a lot of boost to make power, but really needs both a transmission improved kit and a mild reprogram to be a fun truck to tow. Fuel mileage around town was about 15, towing hard to say because it depends on winds, weight, trailer, etc
2007 6.0 - I was not impressed, head gasket issues initially when new, but real issue is it needs boost to make the torque of a 7.3. That being said, runs circles around a 7.3, but uses fuel to do it. Still, relatively easy to work on, runs real hard when you get it right, also likes electronic tuning. Was about 14.5 mpg in town, watch the trend. Had an issue with shimmy (6.0 guys call it death wobble, Ford took it back and I got a 2008)
2008 6.4 - I loved this truck, engine is fun, sounds great, quiet, does not pull much without boost. Fuel hog....has a DPF which means you need to regen now and again, and until you get used to it, you won't believe how crazy it can sound. You can eliminate the DPF with a tuner, can reporgram the tranny unlike earlier, pulls strong even stock. Hard not to like the engine and tranny, but not good on fuel. A solid 13.5 mpg in town, but the kicker is, can't even change a valve cover gasket without pulling the cab and nose. Nice thing is, Ford designed the cab and nose to be unbolted from the bottom. I had a hard time trading this truck, other than mileage I loved it, but it was not easy to work on the engine the way they pack it in
2013 6.7 - I had this one for a week. Real bummer too, lost money, but in the end happy. Engine was a MONSTER, quiet as a gasser, like a quiet sewing machine, tranny was awesome, suspension was a bit more bouncy, but many different configurations and the 2008 had all the heavy F250 goodies and this one didn't. The issue was the seats were miserable in 2 ways. As a 230 lb guy, I was never comfortable, but more than that, the memory stuff and dash all started going crazy. Seat would move driving down the road, pedals would move, gauges were wonky. They said in 2013 that they were stumped, and offered me another truck. Mileage seemed great, but also needed the cab removed for work. That truck felt like a big block car, it was fast and fun, but jumped ship to see how it towed, I assume awesome
Where I ended up...
2013 6.7 Cummins - I wanted to hate this truck, but it is by far the best truck I have owned, has been all over the US and I see why they have a cult following. not drag race fast like the Fords, but even with 11K on the bumper, the Fords don't out pull me on a hill. 16+ MPG in town, 22-24 empty on cruise on the highway, engine uses more compression and less boost and less RPM to make power, so it rarely shifts and you just hear a little whistle when the cruise tells it to hammer down. I town in the passing lane when required and I just can't imagine getting rid of the truck. Solid flat tappet, I closed the lash up as much as I could when new to get a bit more on top (I was used to the Fords that rev a LOT higher). It clucks away at idle, but quiet inside. I literally have done nothing to this truck other than basic maintenance, but if I do have to, I can reach and touch everything. Regen you can't hear, ever know if it does it, but it does. The Ram also is about a foot shorter and the seats are awesome, fits in the garage a little easier
One negative - it is very difficult to unnaturally program a Mopar. You have to buy a tool to hack the computer, and then you have to buy the program and another programmer, but by hacking, you really leave tracks even if you return to stock for whatever reason. That being said, the guys are making ridiculous torque. Mine is an 850 ft lb version, and I think Cummins are approaching or at 950 ft lbs now, so I kept this one absolutely bone stock other than a little electronic box to make the throttle pedal act more linear and the valve lash, but even with that, I left the lash at the tight side of stock on the exhaust side and barely tighter than stock range on the intake, to make sure the valves had time to dissipate heat when towing
I hated to jump ship, and intended to switch back as not only a long time Ford guy, but also long time Ford diesel guy, but I can't imagine myself in a different truck after this Ram