Are you sure your global settings or widget options limit is not set to `1`? The default is 10. See attached.
Are you positive you're not using `[testimonials]` list shortcode versus `[testimonials_slider]` for the rotation shortcode?
Are you positive you're not using `testimonials()` list theme function versus `testimonials_slider()` for the rotation theme function?
Is jQuery is included twice? Once by WordPress and again by a theme. Remove the jQuery version included by your theme and you should be fine.
Is jQuery running version 1.10+? If not, then your theme is probably overriding WordPress's inclusion. Look to disable your theme's jQuery inclusion like shown.