UPDATE:
Here is how I ended up solving it in case this helps anyone else.
After the above code and before the final I added:
if (isset($_GET['viewall']))
{
function view_allposts( $query ) {
$query->set( 'posts_per_page', -1 );
}
add_action( 'pre_get_posts', 'view_allposts' );
}
if(!$_GET['viewall']){ ?>
<a class="numbered" href="<?php echo add_query_arg( array( 'viewall' => "true" ), get_pagenum_link(1) ); ?>">Show All >></a>
<?php } ?>
Works perfectly! Thanks for your help on this Kaiser, although I used a different solution I learned a lot from the links you provided.