Click & Ship Shipping option not being used

I have a 1.3.8a shopping cart. The shipping module is not figuring the postage right. a four ounce item is costing $13.00 to ship, but it only costs me $5.00 using click and ship, which is my favorite way to ship. How do I fix this, so that the correct postage is figured. My shopping cart was built by a programmer, is this an issue I need to upgrade with the Post Office?

Zen Cart has a USPS shipping module built-in that allows you to use calculated shipping directly from the USPS server. You need to setup a web tools account with USPS in order to use it. Once you've done that you would enter the info they provide in to the module settings.

PS: Also check the settings and see if there's a handling fee entered.