We have 37 episodes, and it only shows the last 2
Only some of the podcast posts in the feed have so called enclosures. podPress adds these elements automatically to feed items. But only if you the media files via the podPress form which is usually displayed below the post editor box (when you add new/edit posts).
Also if you would add a media file URL to a blog post then WordPress would usually add such an enclosure element automatically when you save or update the post. WordPress would in such a case a custom field to the post. (You can display the custom fields box below the post editor (http://codex.wordpress.org/Custom_Fields#Usage) by activating it in the Screen Options (see small grey box in the upper right corner of the WP admin interface)).
How do you add episode files to a post?
I looked at the post of Episode 37 an 36. 37 has and 36 has no enclosure. Both pages show an mp3 player and some download links. The player is from the WP Audio Player plugin and not the one which podPress displays and the download elements are also no podPress elements.
That is why I guess that the episode haven't been added to the posts with podPress.
A further guess is that the post of episode 37 has and custom field with the name enclosure and episode 36 has not such a field.
Please, control whether this is the case.
Add the episodes with podPress or make sure that the posts have at least an custom field with the custom field name enclosure and the regarding custom field values. If you use the WP Audio Player plugin then look into the settings of this plugin. If I remember correctly that plugin has also settings regarding the enclosures.