There's a misleading statement in the Shopify shipping guidelines where they advertise UPS Ground as part of their integrated shipping service, but don't disclose a "limiter" they built in. The publicly available UPS Ground service accepts packages that exceeds 150 lbs in dimensional weight, but not in actual weight. UPS just charge a "large package surcharge" in the case of dimensional weight exceeding 150 lbs.
Shopify however, have modified their UPS Ground offering by limiting you to 150 lbs in dimensional weight. This however is not disclosed anywhere in their shipping guidelines.
Would be great if Shopify could integrate the full UPS Ground Parcel service or correct their misleading literature.