My 99 Blazer wont disengage from 4hi back into 2hi, its making the clicking sounds and i can move the driveshaft by hand while its in the process of going from 4hi to 2hi, but it just freezes back up.

it goes from 4Hi to 4Lo with no problem, but when i (from neutral) try to go from 4Hi to 2Hi the 2Hi light blinks but does not engage. Help please!

Ive tried going in reverse to unlock the hub, which is what did the trick on my 87, but that doesnt do anything...

 

Sounds like the typical encoder motor fault... Try disconnecting the battery and see if it resets back to 2HI.