Flash wont work properly with Canon5D mark III

[scooterthepup]

I have 2 Bower flashes ETTL they both worked fine with my 7D . I just purchased a Canon5D mark III, with flash in TTL ( automatic mode) in every setting with different lenses, in fully automatic mode all the pictures are way over exsposed, I have to turn down the flash setting on the camera to -3 and -3 on exsposer to get a decent pic. I called both Cannon and Bower they both don't have a clue . thanks