The rate details are stored in their own object with each quote line item. The rate details can only be pulled after they've been queried from the shipping api. Try something like this, and then check for your values again:
$_quote->getShippingAddress()->setCollectShippingRates(true);
$_quote->setTotalsCollectedFlag(false);
$_quote->save();
Enterprise Architect
800-207-1221
https://merchantprotocol.com
Magento Extension Developers