Usually most of the bigger stations have at least one Diesel pump, the smaller "compact" stations often don't. I don't think you'll have any problem along an interstate finding Diesel, just watch where the trucks are going.

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1985 300D Turbo ~225k
2000 F350 (Powerstroke) 4X4, SWB, CC, SRW, 6spd ~148k
1999 International 4900, DT466e (250hp/660 ft/lbs), Allison MD3060 ~73k