[Hersbird]

When you say local postmen in all those oddball cars, they are rural carriers. Some rural carriers get assigned a postal truck but most just get paid per mile and can use whatever tickles their fancy. City carriers use the Grumman LLV, or the Ford version the FFV, some kind of minivan (white with the standard paint job), or sometimes a bigger box, step van like UPS uses. We also have a few 9 ton cabover trucks as well.

I don't think they are neglected as far as maintenance just they are plain used up. They say the transmission have been rebuilt so many times the rebuilding company can't get them in tolerances anymore and won't warranty them.
I would think a hybrid would be ideal, i just don't think most anything will stand up to the abuse a mail truck sees. The slow stop and go for hours and hours on end. On and off 100's of times a day. Bouncing around on chains in the winter and rutted potholed shoulders all summer. Shifted in and out of park maybe 1000's of times a day. To me the simpler it is the more likely it can last with minimal upkeep. You see the article Fat Charlie posted they are spending 1 billion on maintenance every year. In the spec for the next LLV they want a 5 year warranty so theoretically the 4-5 billion to replace the fleet would be recovered in less maintenance.