I thought you were using it in Canada. Expedited Parcel is time guaranteed, so it works fine for me in Canada.
I use FedEx Ground to the USA as well. Main reason is not cost, but Customs clearance speed of Expedited Parcel. 3-4 weeks wait when standard is 5-7 business days is terrible. I wish I could use UPS since their system for doing labels is better (I wish FedEx did thermal), their service is faster, and tracking is better, but it comes at a cost. FedEx is good middle ground thus far.