Filtering for slugs

Trying to pull up related posts by their slug w/out success. Any suggestions greatly appreciated! Not using the filter extension for this as i don’t see an option for title or slug. Version 5.6.0.5

[ajax_load_more filters=”true” post__in=”foo1, foo2, foo3″ post_in_type=”post_slug” post_type=”post”
posts_per_page=”4″]