Hello. We have a 2002 Trailblazer we just brought into the dealer because of issues with the 4 wheel drive. It wouldn't go into 4 wheel drive. It would only engage in AWD. If we were in 2WD the transfer case would jump right into neutral. We would stop, shift the transmission into neutral. Then switch the transfer case to AWD and back to 2WD and it would engage again. It got to the point it wouldn't engage unless you had it in AWD. The dealer put a new selector switch in and ran all the new updates for the control module. I received call from them saying it still won't shift into 4H. They think it's some sort of a clutch in the front differential? I've never heard of that. Do they mean a clutching system in the transfer case? It seems wierd that it will engage in AWD and not 4WD. Is there another electrical part that could be defective?