Here's how to get all episodes into the feed:
1.) Log into your WordPress site. Hover over the Settings menu on the left-hand side and select Reading.
2.) Change the number in the "Syndication feeds show the most recent" box to the desired number. Click the Save Changes button.
3.) Hover your mouse over the PowerPress link in the left-hand sidebar and select Settings. On the next screen, switch to Advanced Mode if you're not already there.
4.) Click the Feeds tab. In the "Show the most recent" box, enter the same number you entered in step two. Click the Save Changes button.
Also, in the Feeds tab, you can uncheck anything for maximizing the feed and click the Save Changes button. If you've got any caching plugins/services, you'll want to temporarily disable them so the changes will go thru on the feed. You can reactivate them once you've got what you need out of the feed.