If you're already cruising level ground at comfortable road and engine speeds you can't really do a lot better.
Perhaps you want an in between gear from OD and direct that you have now? I doubt it's worth it to install or fun to shift an auxiliary with an automatic in front of it.
Not that you can;t install an auxiliary with an automatic, it's been done before. but not something you'd want to shift on the fly much. The slip of the converter and lack of a clutch to disengage might make it terribly difficult to match speeds and get it back in gear while moving.
Also note that an auxiliary shouldn't be left in OD whine the main transmission is in lower gear gears. The OD should only be used in the higher gears (less torque/stress and heat).
Grigg
