I was evaluating Ubercart for a client and noticed that the USPS Web Tools API is now deprecated: https://www.usps.com/business/web-tools-apis/welcome.htm. I can't see any posted date of when it will be shutdown. Maybe they're providing a long lead time.

The new API uses Oauth authorization so it would be a bit of work to get that working in Ubercart. Just based on that, I'm pretty sure that Ubercart is still using the old API.