General consensus of the Ford owners is to stay with the 7.3 PSD. The 6.ohno, either was very good, or very bad (more bads than good from what I've read). The later models, 99 and up, seem to be pretty good too.
I personally own a 99, F-350 dually, crew cab with 179K miles.

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87 300SDL - 215K Miles !!
99 F-350CC Dually PSD - 190K
86 300SDL - 189K
All on B-100

Definitely unimog

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1983 240D 3.0T 4-speed manual, now sold

1989 Subaru GL Wagon 5-speed Touring Edition

89-93 dodge d250. club cab. Great 5.9L Cummins with the VE rotary style inj pump, is easy to tweak. If you want an auto, go with 91 or newer (they had o.d) Also if possible look for a 91.5 or newer truck, they had factory intercoolers. Should be able to find a gem for under 5 K

For example: http://seattle.craigslist.org/see/cto/1344787770.html

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Regards,
Ian White

1995 E300 Diesel w124 OM606
2014 E550 w212 M278 biturbo

2001 BMW 740i E38 M62 (past)
1981 300SD w126 OM617 (past)