Forgot to mention...  Priority Mail is coming out more expensive than Priority Mail Express.  That is another indication something is not right.

Hi Scott,

Thank you for posting to our forums!

The rate issue seems to be related to Previous Selections.  This means that for each order that you ship, ShippingEasy will remember the carrier, service and packaging type so that when another order with the same list of products arrives, ShippingEasy will automatically default to the previous shipment selections that you made.  You can see more about this here:  FAQs: Previous Selection

I will go ahead and disable this feature from your account though I will note that Shipping Rules override Previous Selections so you could consider setting Shipping Rules up to apply Saved Selections. 

First, save your Carrier Selections right on the Ready to Ship screen by following these steps:  How to: Save my Carrier Selections for future shipments

Then you can base the Shipping Rules off of requested service or another option.  Here is an example of how to set it up based on requested service:  Best of Rules: Assign carrier selection to a batch of orders per requested service

These articles may be helpful as you get the Shipping Rules set up as well:
FAQs: Shipping Rules / Mapping
What Shipping Rules are available for set-up?

Also, I was able to get a lower rate on the order on your Ready to Ship screen by removing the dimensions.  You could try that for your other existing orders.  New orders that sync should not run into the issue since I disabled the Previous Selection feature on your account.  If we can assist further, please post again.  Thank you!