USPS are soon to discontinue their old RateV4 shipping calculator. In response to this we have released a free new USPS extension to connect to the current API (3.0). We recommend that all our US merchants upgrade to this extension.
More Information: https://www.cubecart.com/extensions/shipping-methods/united-states-postal-service-usps-api-3-0
Public forum discussion can be found here. To use this new extension, merchants will need to obtain a new Consumer Key and Consumer Secret.