I'm not sure about futaba, but on most radios (and I suspect futaba is no different), the stick tension is adjustable.

Edit:

As is stick height, which may also be causing you some grief. If the stick is too tall, then you can have problems at neutral (assuming you are a thumb's only flyer) because that is where the stick will be "tallest." Try shortening your stick height, and, if that fails, try alleviating some of the stick tension.