Heirloom review for UPS Shipping (Official)

I want to use this app, but it ALWAYS incorrectly rates our shipping costs even as we've tried multiple times to synch it to our UPS account. We've become accustomed to this. However, the app often loses synchronization with Shopify and we are unable to fulfill orders received in time for EOD shipping. Kind of sucks when the UPS driver has to come back the next day because the app doesn't work.