I see the problem.
The line of code in the USPS include file:
if (strtoupper($USPS_Parameters["CarrierCode"]) == "PARCEL" && strtoupper($USPS_Parameters["CarrierCode"]) == "ALL") {
must be wrong... my guess is that it should be:
if (strtoupper($USPS_Parameters["CarrierCode"]) == "PARCEL" || strtoupper($USPS_Parameters["CarrierCode"]) == "ALL") {