Hello,
Sorry for the late reply, I tried to reproduce it on my end but it worked fine. Note that if your rates are too low, it can be coming from the fact that USPS is automatically grouping the product on packages until it reach the package dimension/weight limit. A solution can be to only use one package per product and edit the file "plugins\hikashopshipping\usps\usps.php" and change this line :
$package = $this->getOrderPackage($order, array('weight_unit' => 'oz', 'volume_unit' => 'in', 'required_dimensions' => array('w','x','y','z')));
By :
$limit['unit'] = 1;
$package = $this->getOrderPackage($order, array('weight_unit' => 'oz', 'volume_unit' => 'in', 'limit' => $limit, 'required_dimensions' => array('w','x','y','z')));
If it didn't fixed your issue, is it possible to have a temporary back-end / FTP access to your website so that I can directly test and fix it ?
You can send it through our contact form :
www.hikashop.com/support/contact-us.html