Originally Posted by: Ryan Heldt 
We have a customer that sells a particular item which weighs 56 lbs and is 56" x 14" x 14". In other words, it's big and heavy...One of the sites is on BV2013 and the other was recently updated to 2015. Anyway, the rates coming back from UPS on each of these sites is wildly different for this item. For example:
Qty | Site 2015 | Site 2013
1 | 45.74 | 49.08
2 | 180.62 | 98.16
3 | 420.08 | 147.24
The product details (weight, dimensions, etc.) are exactly the same between both sites. The only difference between the sites is on the BV2015 site, I have the "Don't use package dimensions, only weight" option checked. Otherwise, the rates are even higher -- substantially higher (3x or more).
...I know some changes were made with respect to dimensional shipping in BV2015, but with that part of it shut off, I'm unsure why there's still a discrepancy?
If the cart/order only contains one item, with a quantity of 1, the rate difference is probably just the difference between sending UPS the dimensions or not.
Once you move to multiple items (that don't ship separately), the packaging algorithm is used to calculate the shipped package size to use for the shipping estimate. The algorithm that BVC 2013 (and 5.X) uses can be very inaccurate. So, you're probably dealing with the difference between an inaccurately calculated box dimension vs. no box dimension.
In BVC 2015 you can select your packaging dimension calculator (Options >> Site Settings >> Shipping). If you set the dimension calculator dropdown to the "Extended Dimension Calculator", it should calculate package dimensions just like BVC 2013. Doing that, and un-checking the "Don't use package dimensions, only weight" checkbox on the UPS shipping settings, should result in the same rate.
That said, the "Extended Boxing Dimension Calculator" in BVC 2015 is typically much more accurate.
Originally Posted by: Ryan Heldt I do know after the second package gets added I start seeing messages in the BV2015 site's diagnostics that read "Large Package Surcharge has been added to Package X", which probably explain the massive jump from 1 to 2 items. I'm not seeing that at all in the BV2013 site's diagnostics.
Are you getting real-time rates from any carriers other than UPS? If not, I'm not sure why you would be getting that message only in BVC 2015 if you're not sending dimensions to UPS.