Starting with the hardest GT3 to drive probably doesn't help. The GT3's blip for you so no need for that. As skill said, you don't gradually come down the gears in the GT3. Get hard on the brakes and bang down the gears as fast as possible. They stop so quickly that the gearbox shouldn't go into protection mode by you trying to go down gears too quickly. Macca is tail happy as it is and fixed sets aren't great. Maybe try the AMG for now which is bit more stable or the the Ferrari?