X5 Towing- Problem with Reverse

[KenFox]

Hi all,

I recently bought a 2012 35i with about 80k on it, and tried to tow my boat for the first time. We live on a moderate hill, and I was trying to back the boat up the driveway. The X5 would not move the boat- with the pedal to the floor. The engine just bogged down a lot. One one attempt, I was able to inch up the hill just a bit with the engine revving higher than the other attempts. I stopped after a few seconds though. The trailer weighs maybe 5000 lbs, so within the capacity of the X5. Plus, it seems to tow okay moving forward- I was able to go up the same hill forward towing the trailer with no problem. I do know I may have something wrong with the transfer case (front tires skip when turning tight at low speeds), but I haven't read anything about a transfer case causing the symptoms I have with towing. Problems with the trailer have been ruled out- I had the same issue with 2 separate trailers.

I'd appreciate any ideas. Hoping not to have to fix both the transfer case and transmission.

Ken