99' Yukon encoder motor

Our 1999 Yukon will not disengage from 4 wheel drive, since changing it into 4 wheel drive for the snow this past weekend. We replaced the front end accuator and it still won't change back into 2 wheel drive. We took it to a GMC dealership and they said that the encoder motor is bad and needs to be replaced. The part alone is $600! Is it possible it may be something else?

Thanks for your help.

I would check the part stores for a reman t-case motor, you should be able to get one for about 1/4 of the price.