My truck runs and shifts fine, but when it shift to OD you can hear what sounds like a loud rear end whine. You can left off gas and it goes away, start at about 50, ease back in and you can hear it start again. When whining you can give it more gas or pull it in D and it will go away, leaving only the slight rear end whine. Is this something that will require a complete rebuild? Need truck for a 2k mile trip next month and I am not sure what to do.