Hi alrwebber,
First, you need to select the “background image and excerpt” in the slider display options. Then, on each page/post you are displaying, there is a menu option below the editor called “graphene page-specific options”. Here, you need to choose Custom URL for the slider image and then enter the URL of the image in the box below.
You may need to experiment with image sizes.
You can view a similar slider on my site HERE. My images are 660×200 px.