After fighting with chat/phone support for months, I finally emailed jeff@amazon with a lengthy message recounting my recent shipping experiences with USPS. They removed USPS as an option from my account. Everything now comes from UPS/FedEx.
It may be worth noting that I spend roughly one order of magnitude more than their average prime customer annually (work equipment).
It may be worth noting that I spend roughly one order of magnitude more than their average prime customer annually (work equipment).