How far and at what speed can one Drive in 4Lo range on highways

 

You can drive as far as you have to if the road is pretty straight. Don't make any really tight turns but as long as the center diff isn't locked you should be OK.
You are probably limited to about 25 to 30 mph. You may be pushing the rev limiter much beyond that.

 

Thanks for the reply. Much appreciated. My LX 570 is stuck in 4Lo and I need to get it to a service centre so had some conflicting information about driving it there about 20 miles.

 

I assume you have tried rocking it back and forth in forward and reverse on level ground then putting it in neutral and trying to switch back to 4hi. Sometimes it just needs some movement to unbind. (unless this is an electrical issue)