You are definitely getting very good advice here so far. Someone already mentioned the Turbo Diesel Register - very good idea. A wealth of info there and their buyers guide is a must read. I've been a member since before I bought my truck and it's worth every penny. Love the magazine too. Ditto on buy a southern truck if you can. Mileage is not that big a deal, but a truck of that age that spent every winter on salted roads will have rust.
Here's a question for you. Do you like to or are you willing to turn wrenches? Personally, I do and as a result, my 2001 has been incredibly inexpensive to operate despite 255k on the odometer currently. The fact is, when you get to that age/mileage, things will come up. If you can do-it-yourself, most of it will be minor and inexpensive. If you have to drag it into a shop every time, the cost will start to add up.
Here's an example. A few years ago, I noticed that when I started the truck, the starter didn't always engage on the first try. So, off to the Turbo Diesel Register forum for advice. I quickly find out that on high mileage trucks, the plunger and contacts in the starter wear out and will eventually no longer make contact. It starts out intermittent but eventually they will wear out to the point the engine can't crank. If you took it to a shop, they'd replace the starter, probably to the tune of $350-500. I found out from TDR that a company called Gould makes a re-build kit for about $25 and your starter will be as good as new. They provide detailed instructions and a DVD showing how to do it. Not hard at all, 2 hours tops and you are back in business with a basically good as new starter.
I will say, I love my truck. I love working on it and keeping it in top condition. At the hint of any problem, I immediately start looking into it and take care of it before it becomes serious or strands me somewhere. So far, knock on wood, it has NEVER stranded me. It's an 01 and I've owned it since 07, everything I've done has been inexpensive. The most money I've ever spent on it at one time was new tires and new batteries. I will say though, right before I bought it, the previous owner rebuilt the transmission (5 speed stick shift) and replaced the a/c compressor. That's part of why I bought the one I bought. Two expensive items that were zero mileage for me. Also, he had done the clutch about a year earlier. I felt like most of the potential "big stuff" was already done.
The bottom line I think is this. When you buy a truck with that mileage, you are getting A LOT of truck for the money! Take care of it and it will work hard and last a long time for you. You just can't beat a Cummins 5.9. There are many out there with 500k and even some with over 1,000,000 miles still going strong!
