Flusher,
There is a lot of good advice here, as well as opinions. There is a lot more of it (good info, and opintions) in this thread that I started when I was searching for a truck:
http://www.tractorbynet.com/forums/trailers-transportation/153238-7-3l-powerstroke-5-9l.html
For several reasons, I wanted a diesel. With a projected use of 3-5k miles per year, many advised the the Ford V10, and the GM 8.1L vs. a diesel, and all for good reasons. My choice was more than just about simple economy. My wife and I try to be green, and both cringed at the thought driving a vehicle that gets, at best, unloaded on the highway, 12-13 MPG. Of the big three, consensous seems to be that the Cummins is the best engine, but in a not-so-good package. I've always been a Ford fan, and have the benefit of having two nephews that are technicians at a local Ford dealership, one of which is a diesel tech. From what I understand, the Dodge/Cummins package is a 500,000 mile engine in a 100,000 mile truck, and the Ford Powerstroke (International/Navistar) is a 300,000 mile engine in a 300,000 mile truck.
I was looking in the $10-15k range, so I started looking at 1999-2003 Ford F-250's with the 7.3L Powerstroke. Because the truck is going to be used to pull a camper on family vacations, a crew cab made the most sense, because of overall length, I was looking for a short bed truck. I also wanted under 150k miles. I soon learned, as others have mentioned here, that the F-350, and F-250 are basically the same truck with minor suspension differences. In my search, I found that often, the F-350s where priced the same or LESS than equivalent F-250's, and there were more crew cab F-350's than F-250's.
I wasn't initially looking at 2003-2007 6.0L trucks, as they were getting too new to be in my price range, but also, because the 6.0L has a bad reputation. I was assured by my nephew (Ford diesel tech) that these problems were resolved by 2005, and that if I found a good 2005-2007 truck for a good price, I should seriously consider it. The 6.0L engine makes 325 HP/570 lb*ft, vs. 275 HP/520 lb*ft -- 50 more HP, and 50 more lb*ft -- what's not to like! The other benefit to the 2003 and newer trucks is the "Torque Shift" 5 speed automatic transmission, which is a huge improvement over the older 4 speed unit. The Super Duty trucks also got an improved front suspensions (coils instead of leaf), which gives them a better ride, and a 5-foot smaller turning cirle.
The main thing with the 6.0L vs. the 7.3L is maintenance. Change the oil every 5k, and the fuel filters every 15k, and drain the water out of the HFCM (fuel filter/water separator) monthly. Because of the bad rep. of the 6.0L, you might find some of the in the same price range aas the 1999-2003 7.3L trucks.
I ended up finding a 2006 4WD F-350XL crew cab long bed with 113k miles for $13,500. Most of the other trucks on my list were 1999-2001, and $12k-$17k. One consession that I had to make, was that it is a lower-end XL truck vs the XLT's and Lariats that I was looking at. This means no power windows, locks or mirrors, no door pockets, plain bench seat w/o center console, etc. My truck does have AC, cruise control, and the very nice integrated brake controller (which is an option, and wasn't available on the earlier '99-'03 trucks). The upside, is a truck that is half the age of the others I looked at, and has likely all highway miles (>25,000/year). Also, as stated above, with the revised front suspension, the turning circle of this truck is about the same as a crew cab short bed, so I get the additional cargo space of the long bed, but the same turning radius of the earlier short bed trucks I was looking at. I'm going to make some stake sides, so when I get firewood, I can make use of the 11,200lb GVWR/3900 lb payload this truck has, haul a full cord of wood at time in the bed, and another in my trailer.
After purchasing, I promptly sent the truck to my Ford diesel-tech nephew to flush and fill both the transmission and cooling system, as well as give it a good check over. I'm also change out all the rest of the fluids as well (engine oil, transfer case, differentials). What ever truck you get, you should do this with once you get it. Automatic transmissions need to have the fluid changed at least every 30,000 miles, no matter what the manufacture states. This info comes to me from a friend of mine who rebuilds automatic transmissions for a living.
All the big three make good trucks, some better than others, but when buying a used truck, the most important thing is probably how it was maintained. As others have stated, get a prepurchase inspection from a qualified technician, and get a carfax report (I still have 2 weeks left on my 30-day subscription if you want to me to get the carfax for you). Good luck with your search!
Jay\