Magento – Can’t override Sales Shipping model file

I try to change the shipping total title in the checkout review table. I have found where the label text is constructed,Mage_Sales_Model_Quote_Address_Total_Shipping::fetch() method is where I want to override the text, the method looks like this:

public function fetch(Mage_Sales_Model_Quote_Address $address)
{
    $amount = $address->getShippingAmount();
    if ($amount != 0 || $address->getShippingDescription()) {
        $title = Mage::helper('sales')->__('Shipping & Handling');

        /** the following if block is what I want to remove as I don't want
         *  extra text in the parenthesis
         */
        if ($address->getShippingDescription()) {
            $title .= ' (' . $address->getShippingDescription() . ')';
        }

        $address->addTotal(array(
            'code' => $this->getCode(),
            'title' => $title,
            'value' => $address->getShippingAmount()
        ));
    }
    return $this;
}

Please notice my comment in above code, I try to do it by overriding the class in my local directory, I have done it many times to other model classes, never had a problem, but I am stuck at this one…

My module config.xml (app/code/local/MyCompany/Sales/etc/config.xml)

<?xml version="1.0"?>
<config>
  <modules>
    <MyCompany_Sales>
      <version>0.1</version>
    </MyCompany_Sales>
  </modules>
  <global>
    <models>
      <sales>
        <rewrite>
           <quote_address_total_shipping>MyCompany_Sales_Model_Quote_Address_Total_Shipping</quote_address_total_shipping>
        </rewrite>
      </sales>
    </models>
  </global>
</config>

app/etc/modules/MyCompany_Sales.xml

<?xml version="1.0"?>
<config>
    <modules>
        <MyCompany_Sales>
            <active>true</active>
            <codepool>local</codepool>
        </MyCompany_Sales>
    </modules>
</config>

My own model class file: (app/code/local/MyCompany/Sales/Model/Quote/Address/Total/Shipping.php)

class MyCompany_Sales_Model_Quote_Address_Total_Shipping extends Mage_Sales_Model_Quote_Address_Total_Shipping
{
  /**
   * Override to get rid of text between parenthesis
   */
  public function fetch(Mage_Sales_Model_Quote_Address $address)
  {
      $amount = $address->getShippingAmount();
      if ($amount != 0 || $address->getShippingDescription()) {
          $title = Mage::helper('sales')->__('Shipping & Handling');

          $address->addTotal(array(
              'code' => $this->getCode(),
              'title' => $title,
              'value' => $address->getShippingAmount()
          ));
      }
      return $this;
  }
}

Please help! I am running out of ideas. I reaaaly don't want to make changes to core files.

Many thanks!