Pivot Table Grouped #'s (not dates) not placed in sequential order when Slicer is created

Hello,

I have a pivot table in 2013 where I have grouped a field of numbers from 0 to approx 2000 by 3 but stopping at 21. I would expect the slicer to show from top to bottom as 0-2, 3-5, 6-8, etc. Instead it is showing as 0-2, 105-107, 1071-1073, etc. How can I get the slicer to reflect in a standard sequential order? I have checked and all of the data is in a number format on the spreadsheet. Any help would be appreciated.

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