Hi @BSubBlanks
Thank you for sharing that screenshot and the additional information about your shipping rate issue. i can definitely understand your concern about your shipping rates when you are having to pay additional fees out of pocket.
In this situation I would recommend connecting with our live support so that our shipping team can review the account and help provide some insight into this. Generally speaking, I do see the USPS rates matching up appropriately as long as the checkout weights of the package are matching. From your screenshot, it does look like that is setup properly.
The only other thing I can think of is that the USPS rates themselves are fluctuating between when the customer is placing the order and when you are going through to buy the shipping label.
To contact our live support please follow this link: Shopify Help Center - Contact Support, sign into your store account, search for “incorrect shipping rate calculations” and use the contact support button at the bottom of the search results to see all our live support options.