I need to back up a steep driveway with my camper on so I thought putting it in 4WD Lo would be perfect, but it doesn't seem to work? I tested this out in a local parking lot. It goes into Lo range just fine and works great in Drive, but when I put it in reverse it goes back to the taller gearing? Hubs are manual and they were unlocked. Is this how the BW1356 is suppose to work, or is something broken? Any insights here would be greatly appreciated. Thanks. Jim