I traded in my 02 Ranger FX4 (sweet little truck, but just too little) on an 06 F350. Quite a step up. Funny thing is, it gets about the same mileage - that Ranger with the 4.0 V6 sure sucked the stuff up. It got maybe 16 on the road, whereas this F350 does 17-18. In town, the F350 does get thirsty, but it's a four ton truck. Going to take some juice to get it moving.
Couple of things to think about...
In 05, the F250 and F350 went to a coil spring front suspension. Ride was substantially improved. I love the way my F350 rides. Even with crew cab and dually rear, it is smooth. Hard to believe this is a one ton truck. The sunroof and leather seats don't hurt, either. If you're going to drive a truck, may as well be a comfortable one. If you're thinking about a 6.0 PS, it's worth a bit extra to get at least an 05, they made a lot of improvements that year. My 06 is showing 73k miles. So far, the only problem was replacing one injector and EGR clean at 50k miles. Otherwise, it's been trouble free and just plain terrific.
Nothing wrong with Chevy, they make a fine truck, but 4x4 with independent front suspension is definitely higher maintenance, a lot more things to go wrong. I'd suggest you check out the ride on an 05-06 4x4, before taking on the extra maintenance. Also, if you want to lift it later, IFS poses some issues, not the least of which is those expensive CV joints you'll be wearing out.
One thing I particularly like about this big monster is how steady it feels. The Ranger always felt like it was going to tip over, and that's with no lift kit, other than the 1" raise that came with the FX4 package. Nothing is going to tip the F350 over. Crosswinds that bat cars around don't budge this big fellow. Another really nice thing that you've probably already noticed is - elbow room. I always felt cramped in the Ranger, while I can really stretch out in the F350. With crew cab and long bed, parking or driving in tight spaces calls for a degree of planning, but you get used to it pretty quickly.
And you get something else - respect. The other motorists are decidedly more polite when I'm rolling around in Big Duke. Most people seem to realize that the laws of physics outrank the traffic laws: a four ton truck is not something you want to get hit with.