Mine runs like a dream, I have had mine since the worlds where I ran it for the first time and loved it ever since.
I don't use drag brakes, I don't like how they work, I just brake if needed manually.
you could try changing the brake strenght and the drag brake setting it might help it.
I just use all the default settings, model2, brake2, drag0. I have not even tried model4 with the 'engine mapping'