So, below is the code I used to get this working the way I wanted. I had to learn a little PHP from my in-house source
<?php
$args = array(
'post_type' => 'attachment',
'numberposts' => null,
'post_status' => null,
'post_parent' => $post->ID
);
$attachments = get_posts($args);
if (count($attachments) == 1) {
echo do_shortcode('[gpslideshow w=450 h=354 align=left thumbs=off auto=off caption=off]');
}
elseif (count($attachments) > 2) {
echo do_shortcode('[gpslideshow w=450 h=354 align=left thumbs=on caption=off]');
} else {
echo do_shortcode('[gpslideshow w=450 h=354 align=left thumbs=off caption=off]');
}
?>