[elhigh]

I don't know how hard this would be to do, but is it possible to retrofit a lockup torque converter into your tranny? That'd be good for when you're steady-speed cruising.

If not, then how hard to, say, replace the entire tranny with a new one, maybe with more ratioes plus the lockup?

This is pretty far beyond me. I can take a tranny out and put it back in - doing stuff inside the case is black magic, beyond my reach (so far).