Wiring harness that goes between the body and the rear hatch is a known failure point. Wires get worn from constant bending when opening the hatch. Might check that. What does he mean by "error code 54"? Was it preceded by a "P"? "U"? etc.....that would give us a clue.
I can't believe a tow truck operator would knowingly tow an AWD vehicle the wrong way. Towing companies are registered, licensed and have insurance and thus should know proper procedures to follow. They should have been able to tell right away when they started moving the vehicle on just two wheels that it was AWD.