When an engine sits for prolonged periods of time, you should actually change the oil more frequently than what's recomended. The reason is condensation builds up inside of EVERY internally combustion engine. The oil change recomendations from the factory assume that the engine will go through common heat cycles (normal everyday driving). This is usually enough to evaporate the condensation that builds up (between heat cycles).
Carbon build up is a result of combustion gases getting into the oil. Just like condensation, there is no way to avoid it - but it takes a long time for this to become a problem, and the fact that you use synthetic oil, I wouldn't worry about it. I do suggest to use Castrol Syntec or Moble 1 synthetic oil.
As far as the transmission goes -- in Dodges this is the weak link. Follow the factory recomended service intravals. But if you want "un-official" advice, don't mess with the transmission until 75000 miles or longer.
Monday, January 4th, 2010 AT 8:14 AM