2005 Chevy Avalanche transfer case 4WD

I had the "service 4wd" displayed off and on for three months. The Chevy dealer said they would have to keep it to diagnose. Costs $89 for that. Dealer tried a new dash switch which didn't make a difference. No conclusion. It seemed to be okay to drive but it didn't engage all the time when I tried to put it in 4wd, (electronic). When I went to Tenn. In the cooler climate it would work, where I really needed it.

I've had the same problem with all 5 Chevy's I've owned. They usually replace the actuator valve.

It finally started kicking into neutral when I was driving and before I could get stopped the transfer case would shift back into gear, with a grind and clunk. It would stay in gear with no slippage in 4WD AUTO. As soon as I put it into 2WD it would slip out and back in.

Dealer said it was probably the gears or synchronizes. They said it would need a rebuild. I said if it were synchronizers won't that slip no matter what setting it was in. I put over a thousand miles on the truck since and I have no problem with slippage in 4WD AUTO. I think it's the actuator.

What is your opinion?