We have used UPS Ground Freight for 10 years an it saves $$ when sending more than 8 similar packages to the same destination, we do this through worldship, ShipStation says they can do this but, I can't.

This is what they say in their help section.

UPS Ground with Freight Pricing: Currently only available for U.S.-based accounts. ShipStation does support creating labels using the UPS Ground with freight pricing for multi-package shipments over 150lbs.

This is still considered a UPS Ground service, but it uses the freight pricing model instead of the small parcel pricing model. This is not a true LTL service and no bill of lading is required or provided.

Go to the UPS support site for more information on the requirements for this service or contact your UPS account rep to discuss if your shipments qualify. If they do, review the Additional Features section of our UPS article for details on how to create this type of label