I got the truck with a transfer case that was locking up. So the "dealer" put another one and it stopped locking up but instead slowly rolls while in park and whines and slips on take off almost through first gear and then its fine. After a few months it burned out leaving me stranded out in the middle of no where. I got a rebuilt one from a place called transfer case express. I put it in and after the first day it started whining too but very faint. I have another rebuilt tcase waiting to go in but I need to find out whats going wrong before I mess this one up too.
The rolling while in park should not have anything to do with the transfer case as this is a separate piece of the drivetrain controlled by the transmission. There is a pawl on the end of the transmission shaft (assuming this is the stock 4L60E transmission) that should keep the vehicle in park. As to the whining sound, I would first check to be sure the transmission and transfer case both have the correct amount of fluid in them. This can also be caused by a transmission pump or potentially a torque converter that is going out as well. Lastly, I would also recommend checking the U-joints for excessive play as this can also cause a whining sound as you describe.
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