Having owned several with the Cummins I would look for a 91.5-93 years because they were intercooled. Those years also came with the overdrive automatic transmissions which are well built( think torque-flite with OD) as long as you change fluid and filters AND adjust the bands every 30k. very easy to do. Rust over the windshield by the rain gutter is common and there is no replacement parts for the roof available. Rockers are another area prone to rust but are cheap and relatively easy to replace. Doing 60-65mph I routinely got an honest 23-24 mpg with 3.54 rear axle ratio and got 18mpg around town both being empty, all figures are in a 2wd truck. All in all there a well built diesel truck that are reliable and reasonable priced, no glow plugs only heater grid, filters easily changed, an honest medium duty engine that has been installed in construction and farming equipment for some time. Check out Dieseltruckresources or Cumminsforum for more info.