Today in 4WD low range on the sands, my 1983 Jimmy with N208 transfer case suddenly bumped out of 4WD with a loud clang, the front wheels stopped spinning, and a second later bumped back in, re-engaging 4WD. This happened at pretty high revs, while climbing, and the 4WD lever in the cab didn't move (I think). Where should I start troubleshooting? Any advice appreciated. I've already searched but found choppy info, though I couldn't really narrow down the search words. I would immediately suspect the transfer case, and try looking at reasons it could slip out of gear and then back in. I've never opened one up before so I'd rather hear you guys out first.