Lower gearing? Can anyone actually confirm that SD39s had 65:12 or 64:13 gearing? There would not be any advantage to them having low gearing in the service they were in.

I believe that they were initially ordered with the intention as using them primarily as Tehachapi helpers. IIRC - The first order was supposed to have dual control stands in addition to the full light packages and plows on both endss - making them very suitable to run as single rear helpers. (Weren't some RSD-5s similiarly equipped for the same reason?) One of the SD39's other assignments was working the Jawbone on the Lone Pine Local (but not exclusively). As they got tired, they ended their days on LA Bain transfer drags. Did they spend some time on a hump job in Texas? Too bad they didn't make it through the GRIP program.