I have narrowed this my sitemap issue to this plugin. Although I can't figure out why it's causing the problem.
The sitemap is displaying this in Firefox:
XML Parsing Error: XML or text declaration not at start of entity Location: http://www.mysite/feed/ Line Number 2, Column 1: ^
This article says the issue is caused from blank lines in the PHP.
I disabled this plugin and the issue was gone. I really need to use this so I'm hoping that maybe someone has a fix or some insight on this issue.