I was driving over a Rabbit Ears pass in Colorado at 5:00 am in a snowstorm (of course). I was in four wheel drive. I heard four "thumps"
. After I made it over the pass I stopped for gas and my four wheel drive went out. It runs fine in 2 High, but no four wheel drive. Anybody have any ideas what the problem may be?

Thanks

Check the shift actuator on the front axle. I don't know what the sound was but the actuator is an eletric (12v) thermal linear actuator (TLA) and is prone to failure.

I replaced my thermal actuator on a 93 K Blazer with a mechanical actuator from Posi-Lok, works great.

Yes, if you go to a dealer for a replacement, you will have to buy the up-dated actuator + the harness. The harness is almost as much as the actuator. Total of around $200.00. I found an aftermarket replacement for 59.99+freight. The cable controlled Posi-Lok seems like a good ideal, when you shift that it' a sure thing, no electrics or vacuum to fail.