Does it have documentation for parts replaced? Have you owned a diesel before? There's a great list that someone will post about what to look for. Have you started it cold? If its that clean, offer 6500 and see what they say. Where are you located?
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96 F350 4x4 PSD, CCLB, E40D -> ZF5, 4.10ls, Riffraff 6637, 3" DP to 4" straight pipe, SD 17*, Autometer Phantoms, BTS tunes, 180/80 stage II's, DIY/Rebilld E Fuel, Aeroforce Scan Gauge, On The Shelf - Intercooler/pipes, S369, 350-380HP on the Travis Dyno
97 F350 "The Mare Resurrection"