If you've not yet updated to the latest Animate CC 2017, please do that first and ensure you are on version 184.108.40.206.
This release of Animate comes with improved Animated GIF exporter which is accessible via File Menu > Export > Export Animated Gif... The export dialog opens up; set the desired settings and export!
If you're still getting inferior results, please share your file with us to check it out.
Thanks Nipun - I'll look into that. In the meantime, I found a way of doing it. Saved it as a .mov Quicktime file and imported that into Photoshop. It came in as one movie file on the timeline, but once I saved it as an Animated GIF and re-opened the file in Photoshop, it had saved it down as separate frames. Works like a dream and looks great.
Glad to know it worked for you! You wouldn't need to use this workaround with the new Image/Gif exporter in Animate (2017).