I must admit, I'm not familiar with diesels in particular, but I feel that somewhere in the early 80's the quality and craftsmanship of American vehicles took a nosedive. Like you alluded to in your post, the difference between 70's and 90's US trucks is much more significant the difference between 80's/90's and 00's, IMO. Given that, I'd go with a more modern truck that has seen fewer winters. (Caveat - being a New Englander, the number of winters a vehicle has been through may be a lot more significant to me than it is out your way)