Well, just went out to snow blow the driveway and had to move the Blazer. Now the freaking 4wd is working! Put it into D instead of overdrive and it was fine, don't think that should make any difference. I don't like when things fix themselves.
BTW, it IS working in OD too now. Took a blast down the street in the snow and it was fine. When I turned around in a semi dry area you could feel that it was in 4wd by it bucking in the front, sort of like how a Locker rear feels.
Would think it would be an electrical problem if it "fixed" itself like this.