My experience is with a 99 Rodeo but if it's the same then the hubs are not automatic or manual. The hubs are permanently connected, what allows 2WD/4WD is a vacuum operated clutch on the LH axle, inboard of the hub. This might sounds strange but by disconnecting one axle the front diff does not allow any drive effort to the front wheels. Re-lubing the hub itself will not tell you anything.

Is it possible your vaccum clutch is staying engaged but you only hear it above 30mph? Is your steering more difficult than usual at low speeds?

Seems like you need to check out the vacuum clutch.