miles isn't the best indicator of how a truck is...I read about people with 100k plus on a supercahrged HD and still running strong. Its more important as to the type of driver the previous owner was ans what mods were on it. Stock, for the most part, these engines are strong if propoerly maintained.
If you can get your hands on an OASIS report, service records, mods on the truck, and what type of driver the previous owner was (if you don't know the person, assume he beat on it unless it is an old man), they will tell you a lot more about the vehicle than tthe miles