Hello, harmonyinfotech.
Thanks for your reply. I appreciate your suggestion, but that's not one of the steps outlined in the plugin's installation directions.
The sitemap generates correctly and is recognized by Google. So, I'm really not too sure what's going on. All I know is that the XML formatting is non-existent. I'm not sure if this is fault of the W3 Total Cache plugin, or the Google Sitemap Generator plugin.