I tried all you that you suggest but nothing seems to work.

Here's how Shipping/Packaging is configured:

Country of Origin United States

Postal Code 06776

Enter the Maximum Package Weight you will ship 0

Package Tare Small to Medium - added percentage:weight 0:3

Larger packages - added packaging percentage:weight 10:0

Display Number of Boxes and Weight Status 3

Order Free Shipping 0 Weight Status 1

Shipping Estimator Display Settings for Shopping Cart 0

Display Order Comments on Admin Invoice 1

Display Order Comments on Admin Packing Slip 1

And "Shipping" under Order Total modules:
Order Shipping Cost

This module is installed
true

Sort Order
0

Allow Free Shipping
true

Free Shipping For Orders Over
$100.00

Provide Free Shipping For Orders Made
national
And the UPS shipping module:

Enable UPS Shipping
True

UPS Pickup Method
CC

UPS Packaging?
CP

Residential Delivery?
RES

Handling Fee
0

Tax Class
--none--

Tax Basis
Shipping

Shipping Zone
--none--

Sort order of display.
0

Shipping Methods:
Nxt AM, Nxt AM Ltr, Nxt, Nxt Ltr, Nxt PR, Nxt Save, Nxt Save Ltr, 2nd AM, 2nd AM Ltr, 2nd, 2nd Ltr, 3 Day Select, Ground, Canada,World Xp, World Xp Ltr, World Xp Plus, World Xp Plus Ltr, World Expedite, WorldWideSaver
1DM, 1DML, 1DA, 1DAL, 1DAPI, 1DP, 1DPL, 2DM, 2DML, 2DA, 2DAL, 3DS, GND, STD, XPR, XPRL, XDM, XDML, XPD, WXS