Holy Cow! I found a "solution".
Full Text means nothing. It always uses the summary. My problem was that I was using the deprecated /wp-rss.php
When I switched over to /?feed=rss it worked! I had to go into the database and change wp_options.rss_excerpt_length to 5000 but it works.
If any of the WP team is reading this I'm wondering why the "full text" setting isn't being applied. Also, why is all my HTML formatting gone? My posts are just long run-on sentences with no links or images.
EDIT: Change that to feed://yourblog.com/?feed=atom and you will get all the formatting. Also, Feedburner, doesn't take the feed:// protocol, but if you use http instead of feed, they don't seem to mind.