Jason, we were able to resolve this issue you were experiencing. The problem was the include file reference for the usps.php file. This file include was near line 102, this is above the values that are being set from the return info from PayPal. We moved this line of code down after these values around line 170 and it seemed to get things working.
If you have any further questions or troubles please let us know and we will help you with whatever we can.