You have a default namespace xmlns="http://www.gbxml.org/schema"
.
In your XSLT, just add another namespace, say xmlns:text="xmlns="http://www.gbxml.org/schema"
(you are creating a shortcut of the default namespace).
Add also exclude-result-prefixes="text"
to omit the text
prefix in the output.
Then, change:
<p><code><xsl:value-of select="gbXML/Campus/Location/Latitude"/></code></p>
to
<p><code><xsl:value-of select="text:gbXML/text:Campus/text:Location/text:Latitude"/></code></p>