I drove my 97 jeep grand in 4 wheel hi at reduced speeds around 50 mph a good bit in snow and heavy rain and that was on the same road you drove on, I70 between St Louis and Boulder Co. It had over 240,000 miles on it when I sold it. Transfer case or diffs were on good shape. I was careful to shift out of 4hi as soon as I got out of snow or heavy rain. I have new Wrangler now and will do it the same way.