Thank you so much Red!When I lived in the mountains with my TJ I would do the following in the winter ice storms to make it down into town: Throw into 2WD, Press Skinny Petal On Floor, Place Hand on E-Brake, Use Steering Wheel With Sharp 90deg turns (Only allowed when coordinating with E-Brake Pulls), also and this is important, Saftey Third!
Ignore everything written above and put her in 4WD. Operate at a safe speed. If you want to crawl down then 4LO will get you the lower crawl ratio, but I wouldn't use it heavily on bare roads especially if there are sharp turns.
If it's pure ice, then avoid the route if possible as steering may be decided by the whims of the ice and any weight shifted due to off camber butt clenching from drivers seat.