2006 Ford Expedition / transmission slipping and hearing a whining noise

[Denver102]

Any help will be greatly appreciated. I have a 2006 Ford Expedition. I heard a whining noise then the OD light started blinking, and now every gear slips.
Just trying to find a starting point to diagnose.

Thank you very much in advance! Steve C.

 

[Hamfisted]

RK Transmission Repair - Raleigh