The gearing doesn't change between 2H and 4H, the only difference is whether power is being applied to the front wheels. 4L is the only one that changes the gearing between the transmission and the wheels.
Pathys *are* geared pretty low, but that's because Nissan didn't design them for highway cruising, they designed them for (fairly light to moderate) trail bruising.
If you want lower RPMs on the highway, change the gearing in the differential to a numerically lower ratio. If you do that, though, I'd recommend keeping it *on* the pavement.