Not sure I agree with the "Do not drive in 4wd" statement but that may be for the idiots that don't understand 4wd doesn't stop any better than 2wd when it's slick.
Could also be because all four wheels can lock up in 4wd if you're in a low gear and let off the gas suddenly on ice. Something an experienced winter driver wouldn't do, but there aren't many of those in OK.
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