I have an all time all wheel drive Jeep that serves me well until recently. I now have trouble getting up hills under snowy conditions. On further investigation, I noticed front wheels have no power. So my all wheel Jeep is now a rear wheel drive Jeep. Have no idea when this started. What creates this situation. Is the end near for my jeep? I suspect it's an expensive fix and probably not worth it given the age and mileage. I am curious to understand the mechanics though. It's been a terrific vehicle!