As the manifested load were vehicles of a known type and weight, my guess is part of the load broke loose and shifted aft probably right at rotation or slightly after takeoff, causing the Center of Gravity to rapidly shift aft beyond aircraft control limits. This resulted in a steeper and steeper nose rise, rapid loss of airspeed, and stall. Once the load broke loose and they were airborne, they were doomed.
What an awful tragedy!
I agree. A shifting load becomes far more possible when you consider the load was on wheels.
That's my guess having been a cargo increment monitor in a past life and having worked with numerous load masters.