Have you used the Regenerate Thumbnails plugin? It’s recommended (for all WordPress users) to download and install this plugin when dealing with Image/Thumbnails sizes.
Once you install and run this plugin it will automatically adjust all of your images and thumbnails to the sizes you have specified throughout your theme (including your Slider Settings).
Anytime you make changes to the size of your Thumbnails, make sure and run this plugin. The same goes for this theme and any other theme you use whether it’s Genesis or any other WP theme.
Let me know if that helps.