> Regarding the automatic transmission....Is anyone aware of any reliable,
> available options for modifying the 3rd gear to provide a lower rpm?
> Looking for an overdrive or torque converter "lock-up" in order to 
> increase
> fuel efficiency and reduce engine wear/tear.
> 

Unfortunately, sun-and-planet gear auto transmissions like the 090 are kind 
of pre-engineered for certain gear ratio spreads. There aren't actually any 
discrete "gears" that can be shuffled like in a manual. The whole thing 
could be made "taller" by changing the ring and pinion in the differential, 
but as far as I've been able to tell there's only one AT final drive that 
fits the vanagon, and it can only take one kind of R&P. I suppose one could 
have a new R&P set machined, but man, that would be expensive!
The torque converter situation appears to also be the same way. It's the 
final iteration of an old design and there's no compatible lock-up converter 
that'll fit in its place; and even if there was, there'd be no mechanism by 
which to control the lock up.
As a fellow AT Vanagon owner, I wish it weren't so. At least there's the 
consolation that the auto transmissions are practically indestructable.