USPS Calculations Wrong

[jsi]

I have the following settings under Shipping/Packaging:

 

- Maximum weight 60 lbs

- Package Tare 0.4 lbs

- Larger package increase % 10

 

 

Now under USPS shipping modules I have:

 

- USPS Options: Display weight, Display transit time

- Domestic Shipping Methods: EXPRESS, PRIORITY, PARCEL

- Int'l Shipping Methods: GLOBAL EXPRESS, EXPRESS MAIL INT, PRIORITY MAIL INT, PRIORITY MAIL INT FLAT RATE BOX, FIRST-CLASS MAIL INT

 

 

Lets say I add 36 items that weight one pound each.

 

The total weight in checkout is (1 x 39lbs 10oz)

Parcel Post: Estimated 2 - 9 Days $13.90

Priority Mail: Estimated 1 - 3 Days $22.70

Express Mail: Estimated 1 - 2 Days $78.65

 

However, when I go to USPS to print the label, these prices are waaaaay off.

Parcel 2-9 days for 39lbs costs about $39

 

 

 

Now, Lets say I add 60 items that weight one pound each.

 

The total weight in checkout is (2 x 39lbs 10oz)

Parcel Post: Estimated 2 - 9 Days $27.80

Priority Mail: Estimated 1 - 3 Days $45.40

Express Mail: Estimated 1 - 2 Days $157.30

 

 

 

Why does it do this and how do I fix it?

 

Thanx in advance.