But Gpx Is not downloaded as?

You need to update your themes functions.php file to recognise and allow download of the gps file format.

Add this to the functions.php file for your theme.

add_filter('upload_mimes','demo');
function demo($mimes) {
$mimes = array(
		'gpx' => 'application/gpx+xml',
);
return $mimes;
}